Press-through pack (PTP) or blister pack comprising a cover film formed from polyethylene-2,6,naphthalate resin and process for preparing said PTP or blister pack

Abstract: An easy-to-peel film comprising polyethylene 2,6-naphthalate as the main resin component and having a limiting viscosity (η) of 0.31 to 0.6; a process for producing a stretched polyethylene 2,6-naphthalate film having a limiting viscosity (η) of 0.31 to 0.6; a resin comprising a mixture of polyethylene 2,6-naphthalate resins having mutually different limiting viscosities; a modified polyethylene 2,6-naphthalate resin having three or more ester-forming functional groups as a hydroxy compound; a wrapping film produced from these resins; and a method of wrapping with this film. The film has gas-barrier, easy-to-peel, easy-to-tear and press-through properties, and can be used for various wrapping uses.

Description: The present invention relates to a press-through pack (PTP) or blister pack comprising a cover film formed from a polyethylene-2,6-naphthalate resin. The cover film of the present invention has a gas barrier property and, further, is easy to open and easy to tear and has a press-through property. Aromatic polyesters exemplified by polyethylene terephthalate (hereinafter abbreviated to "PET") and polybutylene terephthalate (PBT) have excellent mechanical strength, heat resistance, chemical resistance and other properties and, hence, have been widely used in various industrial applications. Among them, polyethylene-2,6-naphthalate (hereinafter abbreviated to "PEN") is superior to PET in mechanical strength (Young's modulus and breaking strength), heat resistance (long-term heat stability and dimensional stability), chemical properties (chemical resistance and gas barrier property) and other properties by virtue of the rigidity and plainness of the molecular chain and, in recent years, have attracted considerable attention (Japanese Patent Publication Nos. 29541/1973 and 40917/1973). High-performance films of PEN, which have utilized the above properties, for example, base films for magnetic tapes and capacitor films, are currently on the market. Further, PEN is a promising candidate for use in other applications, that is, as a high-performance packaging material in the field of various packaging materials. Paper, various plastics and the like are currently in use as packaging materials and applied to packaging materials having a gas barrier property, freshness retaining packaging materials, heat-resistant packaging materials, easy-open packaging materials and mischief preventive packaging materials. Regarding easy-open packages, various easy-open packaging materials have been developed such as those using a stretched film, as disclosed in Japanese Patent Laid-Open Nos. 55059/1988 and 96066/1988 and Japanese Utility Model Publication No. 11258/1979; easy-tear packaging materials exemplified by pouches provided with a cut, a scratch, a perforation or an opening tape, as disclosed in Japanese Patent Laid-Open Nos. 52065/1987, 39465/1987, 82965/1988, and 67273/1988; peelable packaging materials wherein the contents are taken out by peeling off a heat-sealed cover, as disclosed in Japanese Patent Laid-Open Nos. 109768/1987, 27254/1988, 96067/1988, and 307073/1988; and easy-open caps. For easy-tear packaging materials, air tightness and an increase in speed have been pursued in bag making/charge packing, and regarding opening, it is a common practice to use a method in which the end face of a bag is subjected to sealer tear cutting so that tearing can be carried out from the bottom, or a notch is provided so that tearing can be carried out from the notch (Japanese Patent Laid-Open No. 39465/1987). In the above methods, troubles frequently occur including that the bag cannot be torn straight, the contents are damaged, or the liquid is scattered. On the other hand, vacuum packaging or retort packaging is, in many cases, inconvenient because a cutting tool should be used or it is difficult to take out the contents from the package because the contents are adhered to the bag. In recent years, easy-tear packaging materials with various ideas being incorporated have been developed. Overlap packages in confectionery and tobaccos are generally provided with an opening tape (Japanese Patent Laid-Open No. 67273/1988) to impart an easy-open property to the packages. In general, the overlap package is produced by a single packaging system, and an easy-open stretched polyethylene (Japanese Patent Laid-Open No. 55059/1988), polypropylene, or cellophane is used in a small thickness (20 to 30 µ m) to impart an easy-open property to the film. On the other hand, for shrink packaging, the material, thickness, packaging machine, package form, and the like for the film used vary depending upon the applications and quality required. Therefore, various easy opening methods exist, and this, together with various technical problems, is one of the reasons why easy opening is not extensively adopted in shrink packages. In general, the stretched film is, of course, easily torn in the stretching direction, and this tendency is particularly significant for a highly crystalline stretched film such as a high-density polyethylene (Japanese Patent Laid-Open No. 55059/1988). Japanese Utility Model Publication No. 11258/1979 discloses, as a synthetic resin film having an easy-open property, polyethylene, polyvinyl chloride, polypropylene, polystyrol and nylon films which have been uniaxially stretched by 3 to 10 times. Such a highly crystalline film, however, has problems including that the cut cannot be smoothly propagated and hang-up occurs in places, the film is locally stretched to render the opening very difficult and feather-like residues occur to deteriorate the image of goods. Although this film can be broken in a uniaxial direction, it is difficult to break the film in a direction perpendicular thereto, so that the contents cannot be easily taken out from PTP (press-through pack) using the film. Polyolefins, such as polyethylene, have a poor gas barrier property and, hence, have a problem that the contents of the package is deteriorated by oxidation. The above plastic packaging materials generally have problems including that 1) they cannot be torn by hand or stretched and torn, i.e., do not have an easy-open property, 2) the gas barrier property is low, that is, the gas permeability is high, and 3) since various materials are used in combination, it is difficult to recycle the materials. On the other hand, PTP's using aluminum as a cover do not suffer from the above problems. Since, however, the blister sheet and the cover are strongly bonded to each other with an adhesive, the separation of the blister sheet from the cover is so difficult that it is impossible to separate the resin and aluminum from each other for recycle. Further, even though the used packs are incinerated, aluminum remains unburned. Further, since aluminum used as a cover in blister packs and PTP's is opaque, any optical test of the contents cannot be carried out from the side of the cover with the blister sheet and the cover being integrally formed. Furthermore, also from the viewpoint of preventing the contents from being kept out of mischief, these packages are preferably easy to open and transparent so that whether or not the contents have been once taken out can visually learn. EP-A-0 225 631 discloses a polyethylene-2,6-naphthalate film for plastic film capacitors having a Young's modulus of not smaller than 600 kg/mm 2 both in the machine direction and in the transverse direction and a degree of crystallinity of not smaller than 40%, and a method for producing said film. US-A-3,875,119 describes a biaxially oriented and post-heat-treated polyethylene-2,6-naphthalate insulating film composition which exhibits not only electrical insulating characteristics but also satisfactory physical properties when used for a long time under high temperature conditions, and a process for the preparation of said insulating film composition. US-A-5,176,861 discloses a polyester resin sheet having a thickness of not less than 125 µm for forming a polyester container, in which a recovered polyester resin from, for example, domestic wastes is used as a raw material having an intrinsic viscosity of 0.45 to 0.70. An object of the present invention is to solve the above problems of the prior art and to provide a PTP or a blister pack, comprising a cover film which can satisfy requirements for gas barrier properties, easy-open properties (including easy-tear and press-through properties) and can be recycled. The present inventors have found that the molding of a polyethylene-2,6-naphthalate (hereinafter referred to as "PEN") having property values falling within particular ranges into a PEN film having property values and degree of working falling within particular ranges provides such a property as to easily break in a plurality of directions including the stretching direction upon the application of force, that is, easy-open properties (including easy-tear and press-through properties) and that the PEN film having such a property is useful as flexible packaging bags, for example, a packaging materials, for example, pouches and small bags, and best suited as cover materials particularly for blister packs and PTP's, which has led to the completion of the present invention. Specifically the above easy-open properties can be realized by providing a press-through pack (PTP) or blister pack comprising a holding portion and a cover film, said film comprising a resin composed mainly of polyethylene-2,6-naphthalate and having an intrinsic viscosity η in the range of from 0.31 to 0.6. According to preferred embodiments of the PTP or blister pack of the present invention, the film may be a weakly stretched PEN film, which has been stretched by 1 to 3 times and 1 to 3 times respectively in the longitudinal and transverse directions, and a strongly stretched PEN film, which has been stretched by 3 to 6 times and 1 to 1.8 times respectively in the longitudinal and transverse directions. In the present invention, the (weakly) stretched films include also a film having a stretch ratio of 1 time in each of the longitudinal and transverse directions, that is, an unstretched film. The present invention provides a PTP or blister pack comprising a holding portion and a cover film, wherein said film is preferably a weakly stretched PEN film comprising a resin composed mainly of PEN having an intrinsic viscosity η in the range of from 0.31 to 0.6, said film having stretch ratios of 1 to 3 times and 1 to 3 times respectively in substantially mutually perpendicular directions and a thickness in the range of from 5 to 150 µ m, and a process for producing said PTP or blister pack. Further, the invention provides a PTP or blister pack comprising a holding portion and a cover film, wherein said film is preferably a strongly stretched PEN film comprising a resin composed mainly of PEN having an intrinsic viscosity η in the range of from 0.31 to 0.6, said film having stretch ratios of 3 to 6 times and 1 to 1.8 times respectively in substantially mutually perpendicular directions and a thickness in the range of from 5 to 150 µ m, and a process for producing said PTP or blister pack. The PEN films according to the invention, when used as a cover for blister packs, can exhibit press-through properties unattainable by the conventional plastic covers used in the art. Thus, they can solve all the above problems of the prior art. Furthermore, the present invention provides a process for producing the PTP or blister pack as defined above, comprising the steps of: providing a resin composed mainly of PEN having an intrinsic viscosity η in the range of from 0.31 to 0.6, stretching the resin at 120 to 270°C in substantially mutually perpendicular directions respectively by 1 to 3 times and 1 to 3 times, heat-setting the stretched resin at 170 to 270°C for 1 sec to 30 min, molding the heat-set resin into a film having a final thickness in the range of from 5 to 150 µm and bonding the film to the holding portion with an adhesive or a heat-sealing agent. Furthermore, the present invention provides a process for producing PTP or blister pack as defined above, comprising the steps of: providing a resin composed mainly of PEN having an intrinsic viscosity η in the range of from 0.31 to 0.6, stretching the resin at 120 to 170°C in substantially mutually perpendicular directions respectively by 3 to 6 times and 1 to 1.8 times, heat-setting the stretched resin at 170 to 270°C for 1 sec to 30 min, molding the heat-set resin into a film having a final thickness in the range of from 5 to 150 µm and bonding the film to the holding portion with an adhesive or a heat-sealing agent. The PEN film according to the present invention can be prepared by molding the above PEN resin alone. Alternatively, it is also possible to produce the PEN film by a production process which comprises co-extruding the PEN resin and a synthetic resin, stretching the co-extrudate under the above conditions and removing the synthetic resin. Furthermore, for some packages, when the contents are hygroscopic or likely to be oxidized, it is possible, if necessary, to laminate a water vapor barrier layer, an oxygen barrier layer or both the above layers. When the contents are heavy, it is also possible to laminate a reinforcing layer comprising a synthetic resin. The blister pack or PTP according to the present invention comprises a cover of the above PEN film and a holding portion (a blister) bonded to the cover with an adhesive or a heat-sealing agent. The PEN film provided by the present invention can be used as various bags for packages. The process for producing the PTP or blister pack according to the invention will now be described in more detail. The resin contemplated in the present invention is a polyester comprising repeating units of PEN. Specifically, the polyester comprises 2,6-naphthalenedicarboxylic acid as an acid moiety and ethylene glycol as a hydroxy moiety. Basically, a packaging material consisting of this resin alone is preferred from the viewpoint of recycling. However, the present invention can be practiced also when other polymers are blended with the above resin. In this case, the content of the PEN resin as a main component should be not less than 60% by weight, preferably not less than 80% by weight, still preferably not less than 90% by weight, based on the other polymers. The PEN resin used in the present invention may be produced by a conventional production process described in, for example, Japanese Patent Publication Nos. 22100/1972, 35260/1973, 40918/1973, 37599/1974, or 945/1979 or a combination of the above methods. Briefly stating, a high-molecular weight polyester comprising ethylene-2,6-naphthalate as main repeating units is prepared using as main starting compounds 2,6-naphthalenedicarboxylic acid or a lower alkyl ester thereof and ethylene glycol. In this case, the process usually comprises two steps, i.e., the first step of providing bis-β-hydroxyethyl-2,6-naphthalate or an oligomer thereof and the second step of polycondensating the compound provided in the first step. The first step is carried out by an esterification of the dicarboxylic acid with the glycol or by a transesterification of a lower alkyl ester of the dicarboxylic acid with the glycol. Any of these methods may be used in the first invention. The transesterification may be carried out by heating 2,6-dimethyl naphthalate and ethylene glycol in at least an equimolar amount, preferably ethylene glycol in an amount of 1.5 to 3 times by mole in the presence of a suitable catalyst, for example, at least one carboxylic acid alcoholate or hydride of a metal selected from the group consisting of Li, Na, K, Mg, Ca, Sr, Ba, Zn, Cd, Al, Ge, Sn, Pb, Ti, Cr, Mn, Fe, Ni, Sb and Co, at a temperature in the range of from 150 to 250°C. The esterification may be carried out by reacting 2,6-naphthalenedicarboxylic acid with ethylene glycol in an amount of not less than about 0.8 time by mole, preferably 1.0 to 5 times by mole. After bis-β-hydroxyethyl-2,6-naphthalate or an oligomer thereof is prepared in the first step, the product in the first step is subjected to polycondensation by heating under reduced pressure in the second step. In the first invention, a polycondensation catalyst, for example, at least one carboxylic acid alcoholate or oxide of a metal selected from the group consisting of Mn, Ge, Sn, Ti and Sb, is added before or after the initiation of the second step, specifically after the first step is substantially completed and before the intrinsic viscosity does not exceed 0.2, and a polycondensation is allowed to proceed. In this case, if necessary, various additives, for example, sliding agents, light stabilizers, weathering agents, antistatic agents, heat stabilizers, light screens and pigments, may be added. They may be added alone or in combination of some of them. In this connection, it is noted that some of the additives may be added in the middle stage or latter stage in the first step and/or second step or immediately before the molding of a film. The amount of the additive used may be 0.001 to 10% by weight, preferably 0.005 to 1% by weight, based on the resin. The sliding agents include organic compounds or inorganic compounds having an average particle diameter in the range of from 0.1 to 10 µ m, preferably in the range of from 0.2 to 3 µm. Examples of the organic additive include high-melting polyethylene terephthalate, polyorganosiloxanes and crosslinked polymer compounds described in Japanese Patent Laid-Open Nos. 117550/1974 and 99948/1980 and the like. Examples of the inorganic additive include LiF, LiPO 4 , MgSO 4 , CaCO 3 , SiO 2 , TiO 2 , kaolin, talc, celite, and the like described in Japanese Patent Publication Nos. 24099/1967, 23888/1968 and 8600/1971 and the like. CaCO 3 , SiO 2 , and kaolin are particularly suitable. The amount of the sliding agent added may be in the range of from 0.001 to 10% by weight, preferably in the range of from 0.005 to 1% by weight, based on the resin. After various additives including the sliding agent and the poycondensation catalyst are added, the second step is initiated wherein PEN having a high degree of polymerization is prepared by a reaction for removing ethylene glycol. For the polymerization reaction in the step 2, with the advance of the reaction, the system is heated to gradually increase the reaction temperature. Specifically, the temperature of the system at the time of initiation of the reaction, i.e., 200 to 250°C, preferably 220 to 240°C, is increased to a temperature of about 270 to 310°C in the final stage. Further, it is preferred to gradually evacuate the reaction system in such a manner that the pressure at the time of initiation of the reaction, i.e., normal pressure, is gradually reduced to not more than 10 mmHg, preferably not more than 1 mmHg, in the final stage. Although the reaction time for polymerization by the melt process varies depending upon the intrinsic viscosity of the resultant PEN, it is 0.5 to 5 hr, preferably 1 to 4 hr because an excessively long reaction time is cost-uneffective and, at the same time, causes a thermal decomposition reaction. Upon the completion of the polymerization by the melt process, the polymer is usually withdrawn from the system by pressurization with an inert gas, for example, nitrogen gas, cooled, cut and brought to an even desired shape. Further, in order to enhance the intrinsic viscosity of the PEN resin, it is also possible to prepare the PEN resin by a polymerization reaction at a temperature in the range of from the glass transition temperature to the melting point, that is, by the solid-phase polymerization. Specifically, a PEN resin having a relatively high intrinsic viscosity can be prepared by heating a PEN chip having an intrinsic viscosity in the range of from about 0.2 to 0.4 obtained by the melt process at a temperature below the melting point of PEN, i.e., 200 to 260°C, preferably 220 to 250°C, in an inert gas stream or under reduced pressure. The intrinsic viscosity of the PEN resin suitable for the easy-open packaging film is in the range of from about 0.31 to 0.6, preferably in the range of from 0.38 to 0.47, still preferably in the range of from 0.4 to 0.45. When the intrinsic viscosity is less than 0.31, the PEN resin is so fragile that it is difficult to mold the PEN resin into a film, while when it is 0.6 or more, the easy-open property is unsatisfactory, making it difficult to take out the contents from packages. Upon the completion of the polymerization, the polymer is usually withdrawn from the system by pressurization with an inert gas, for example, nitrogen gas, cooled, cut and brought to an even desired shape. Thereafter, the PEN resin as a raw material thus obtained is transferred to the step of drying. If the resin is melt-extruded in the presence of water, it is hydrolyzed, resulting in remarkably lowered molecular weight. The purpose of drying is to prevent such an unfavorable phenomenon. In the step of drying, at least the water content of the PEN resin as a raw material should be reduced to not more than 100 ppm, preferably not more than 50 ppm in terms of the water content after drying. The step of drying may be carried out in air or an inert gas stream or under reduced pressure. Drying conditions, such as drying temperature and drying time, drying technique, drying equipment and the like may be those used in the art for drying thermoplastic polymers, particularly polyesters. For example, the drying technique may be selected from a technique where predrying is carried out at 120 to 180°C, a technique where the resin is crystallized to prevent fusing and main drying is then carried out, a technique where drying in air is carried out at 200°C or below because the resin is subjected to remarkable thermal deterioration at a temperature above 200°C and other techniques. Examples of the drying equipment include a vacuum drier, a rotary drier, a fluidized-bed drier, a channel drier and a stationary drier. They may be used alone or in combination of two or more. The dried PEN resin is introduced into an extruder, melt-extruded in the temperature range of from 270 to 310°C and cooled and solidified on a cooling drum to form an unstretched sheet. Two-stage cooling or cooling in water or a cooling medium may also be utilized for cooling (Japanese Patent Publication Nos. 39929/1972 and 10394/1972). Alternatively, the unstretched sheet may be produced by solution casting or calendering. If necessary, the unstretched sheet thus obtained may be stretched. It is also possible to use a method wherein the thickness of the sheet is regulated at the time of extruding and the sheet thus obtained, as such, is transferred to the step of heat treatment. Further, as will be described later, a method wherein a PEN resin extruded at a temperature in the range of from 270 to 310°C is laminated onto a synthetic resin film (extrusion coating (EC) method or heat lamination). In this case, the sheet thus obtained, as such, is transferred to the step of heat treatment without stretching. High-density PE (HDPE), medium-density PE (MDPE), low-density PE (LDPE), straight-chain low-density PE (LLDPE), cyclic polyolefin (COC), PC, PP, PET, Ny, PVA, PBT, and other synthetic resin films may be used as the above synthetic resin film, and, if necessary, an adhesive may be used. The adhesive used may be a commercially available anchor coat (AC) agent and properly selected according to the synthetic resin film. The sheet, which is transferred to the step of stretching, is stretched by 1 to 3 times and 1 to 3 times respectively in mutually perpendicular directions at a temperature of 120 to 270°C (weak stretching) or by 3 to 6 times and 1 to 1.8 times respectively in mutually perpendicular directions at a temperature of 120 to 170°C (strong stretching). For weak stretching, when the stretching temperature is below 120°C, the material is not softened to such an extent as being stretched, resulting in a failure of stretching. On the other hand, when the stretching temperature is above 270°C, the polymer is melted, rendering stretching impossible. For strong stretching, when the stretching temperature is below 120°C, the material is not softened sufficiently to be stretched, resulting in a failure of stretching. On the other hand, when the stretching temperature exceeds 170°C, the orientation and crystallization effects attained by stretching are so unsatisfactory that no easy-open property is obtained and, even though the film is used in PTP or the like, it is difficult to take out the contents from the pack. Regarding the direction of stretch, in the case of weak stretching wherein the stretch ratio is not more than 3 times, both uniaxial stretching and biaxial stretching can realize the easy-open properties because the molecular orientation is not very even. On the other hand, in the case of strong stretching wherein the stretch ratio exceeds 3 times, the molecular chains are oriented in the direction of the plane, so that biaxial stretching provides excessively high film strength, resulting in lowered easy-open properties. In this case, it is necessary to strongly stretch the film in either longitudinal or transverse direction, and a PEN film having excellent easy-open properties can be prepared by stretching in two mutually perpendicular directions respectively by 3 to 6 times and 1 to 1.8 times. Regarding the direction of stretch, any of uniaxial stretching (Japanese Patent Laid-Open No. 159319/1984) and biaxial stretching may be used. When biaxial stretching is carried out, sequential biaxial stretching, simultaneous biaxial stretching or a combination thereof may be used. In the case of sequential biaxial stretching, the film may be stretched first in the longitudinal direction and then in the transverse direction, or alternatively may be stretched first in the transverse direction and then in the longitudinal direction (Japanese Patent Publication Nos. 8338/1959, 1588/1962, and 12496/1964 and the like). Stretching methods may be roughly classified into tentering and tubing. In the tentering method, a molten polymer extruded through a T-die slit of an extruder is set by cooling on a casting drum and stretched in the longitudinal direction by 1 to 3 times or 3 to 6 times by means of a heating roll between a delay (front) drive roll and a quick (rear) drive roll to form a stretched film. The stretched film then enters a tenter, where it is heated with both ends of the film being held, causing the film to be stretched in the transverse direction by 1 to 3 times or 1 to 1.8 times, thereby to form a further stretched film. Thereafter, the stretched film is heat-treated in a back chamber of the tenter with both ends of the film being held, causing crystallization and the fixation of molecular orientation. The tubing method can be regarded as a modified form of the inflation method. Specifically, a molten polymer is extruded in a tubular form through a ring die of the same extrusion as the inflation and rapidly cooled in a cooling bath. Subsequently, the tube is heated by infrared radiation, and air is introduced into the tube to apply an internal pressure, or alternatively the outside atmosphere of the tube is evacuated, thereby stretching the tube in the transverse direction. At the same time, tension is applied in the longitudinal direction, thus conducting biaxial simultaneous stretching. After stretching, the tube is folded by means of a nip roll and then taken up. Alternatively, compressed air may be again introduced while infrared heating, thereby again expanding and stretching the film, and the tube is again folded by means of a nip roll and heat-treated by infrared radiation to cause recrystallization, thereby stabilizing the molecular orientation. Finally, the tube is folded flat, or alternatively may be cut into two stretched films. Which method of the tentering method and the tubing method is selected may be determined by taking the object films and applications and other factors into consideration. It is said that the tentering method is more advantageous in terms of properties of the film, i.e., more even stretching and less susceptibility to wrinkling, while the tubing method is more advantageous in terms of more even molecular orientation. Further, with respect to yield, the tubing method is more advantageous when scrapping of edge of the end portion of the film necessary in the tentering method is taken into consideration. The stretched film is then fed into a heat setting zone for crystallization and fixation of the molecular orientation, where it is heat-treated and heat-set at 170 to 270°C for 1 sec to 30 min. The heat setting temperature is 170 to 270°C, preferably 190 to 250°C, still preferably 200 to 240°C. When the heat setting temperature is below 170°C, the fixation of the molecular orientation and the progress of the crystallization are insufficient, making it difficult to taken out the contents from PTP's. On the other hand, it is above 270°C, no film can be formed because the material is melted. The thermosetting time is suitably 1 sec to 30 min, preferably 2 sec to 10 min, still preferably 2 sec to 1 min. When the heat setting time is less than 1 sec, the fixation of the molecular orientation and the progress of the crystallization are insufficient, making it difficult to take out the contents from PTP's. On the other hand, when it exceeds 30 min, the crystallization proceeds excessively, rendering the film too fragile to provide a packaging material having good easy-open properties. The device for heat treatment is a tenter, and the heat treatment is mainly carried out with the film being clipped. However, it may also be carried out by other methods (see, for example, Japanese Patent Publication No. 3040/1968 and 7159/1969). The heat-set film is taken up by a master roll, slit to a desired size, and then applied to the next step. Thus, a stretched and heat-set PEN film is produced. If necessary, it is further subjected to various surface treatments. Examples of the surface treatment include corona discharge treatment (Japanese Patent Publication No. 12383/1965), UV treatment (Japanese Patent Laid-Open No. 136364/1975), IR treatment (Japanese Patent Publication No. 16317/1968), low-temperature plasma treatment (Japanese Patent Laid-Open No. 80373/1979), graft polymerization (Japanese Patent Laid-Open No. 152913/1984), electron beam irradiation treatment (Japanese Patent Laid-Open No. 113579/1975), radiation irradiation treatment (Japanese Patent Laid-Open No. 132160/1974), alkali treatment, various solvent treatments and various coating treatments. These may be carried out alone or in combination, depending upon applications and purposes. Further, in order to impart several functions to the film, an organic or inorganic material layer having a single or multilayer structure may be laminated onto the surface of the film. The above method can provide a PEN film having easy-open properties. The thickness of a stretched PEN film suitable for easy-open packaging, such as PTP, varies depending upon factors such as the size and hardness of the contents, it is suitably in the range of from 5 to 150 µm. When the film thickness is less than 5 µm, the film is too thin to hold the contents, i.e., broken in transit. Further, a problem arises associated with ensuring gas barrier properties. On the other hand, when the film thickness exceeds 150 µm, the strength of the film per se is so high that the contents cannot be taken out from PTP's, rendering such a film unsuitable for easy-open packaging. For example, when the contents are small objects, such as sanitary articles, medical supplies, office requirements, gardening goods, and carpenter's tools, the film thickness is suitably in the range of from 20 to 150 µm. The larger the contents and the harder the contents, the larger the suitable thickness. When the contents are tableted confectionery, such as candies and chocolates, and pharmaceutical preparations, such as tablets and capsules, the film thickness is preferably in the range of from 10 to 30 µ m, still preferably 10 to 25 µ m. Further, when the contents are button cells, the film thickness is, in general, suitably in the range of from about 20 to 150 µ m. It also varies depending upon the thickness of the button cells. Specifically, it is suitably in the range of from 30 to 50 µm for cells having a diameter of about 10 mm and suitably in the range of from 70 to 120 µ m for cells having a diameter of about 20 mm. As described above, the present stretched PEN film can be prepared by molding of the PEN resin alone. It is also possible to produce the stretched PEN film by a production process which comprises co-extruding the PEN resin and a synthetic resin, stretching the co-extrudate under the above conditions and removing the synthetic resin. More specifically, a PEN resin and an olefin resin, such as polypropylene or polyethylene, or a PET, Ny, PVA, or PBT resin are co-extruded in the temperature range of from 270 to 310°C to form an unstretched sheet comprising two layers of a PEN resin and a synthetic resin. The two-layer sheet is stretched and heat-treated under the above conditions, and the synthetic resin film is then peeled off. Thus, a stretched PEN film suitable for easy-open packaging can be produced. When the contents are particularly hygroscopic or likely to be oxidized, it is possible, if necessary, to laminate a water-vapor barrier layer, an oxygen barrier layer or both the above layers onto the stretched PEN film. The water-vapor barrier layer may comprise any of organic and inorganic compounds. Examples of the organic compound include olefin resins, olefin-modified resins, ethylene/vinyl alcohol copolymer, vinylidene chloride, and ethylene/vinyl acetate copolymer (EVA), while SiO x , Al 2 O 3 , and other inorganic compounds are usable as the inorganic compound. The oxygen barrier layer too may comprise any of organic and inorganic compounds. Examples of the organic compound include ethylene/vinyl alcohol copolymer, vinylidene chloride, and EVA, while SiO x , Al 2 O 3 , and other inorganic compounds are usable as the inorganic compound. When an organic barrier layer is provided, the lamination may be carried out by co-extrusion and stretching at the time of the preparation of the PEN film. Alternatively, after the preparation of a stretched PEN film, an anchor coat (AC) agent may be coated followed by extrusion coating (EC). Furthermore, dry lamination may be used, and it is also possible to adopt coating. The thickness of the organic barrier layer is suitably in the range of from about 0.1 to 10 µm. The organic barrier layer, however, may have a larger thickness when it serves as a reinforcing layer which will be described later. When the inorganic barrier layer is provided, film formation may be carried out after the preparation of a stretched PEN film. Deposition, sputtering, CVD, and the like may be used for the film formation. If the thickness of the PEN film is very thin for the size and weight of the contents and, hence, unsatisfactory in strength to cause a fear of the film being broken in transit, a reinforcing layer of a synthetic resin can be further laminated onto at least one side of the PEN film. The material for constituting the reinforcing layer may be any synthetic resin so far as it can be broken together with the PEN film upon the application of such pushing force or tearing force as to break the PEN film, and examples thereof include olefin resins, such as HDPE, MDPE, LDPE, LLDPE, ionomers, PP, and cyclic polyolefins, polyester resins, such as PET, PC, and PBT, Ny, and PVA. Further, it is also possible to use PEN resins having a high IV value and/or strength imparted by stretching. The reinforcing layer may be laminated by co-extrusion at the time of the preparation of the PEN film or extrusion lamination of the PEN resin onto a reinforcing layer, and dry lamination may be carried out. When the resin to be co-extruded is an olefin resin, a polyester resin other than PEN, Ny, PVA, or the like, it is necessary to extrude an adhesive resin into between the resin co-extruded and the PEN. The adhesive resin may be a polyolefin polymer, a polyester polymer, a urethane polymer, or other polymers. When the PEN resin is extrusion-laminated or dry-laminated onto the above resin, it is necessary to use an AC agent. Usable AC agents include polyolefin, modified polyolefin, urethane, polyester, urethane-modified polyester, partially urethane-modified polyester, polyether, and modified ether polyester AC agents. Ozone treatment at the time of the extrusion lamination can enhance the adhesion between the PEN layer and the reinforcing layer. Although the thickness of the reinforcing layer is not particularly limited so far as the easy-open properties of the PEN film are not deteriorated, it is suitably in the range of from about 1 to 50 µ m. When the thickness is less than 1 µm, the strength of the layer is so low that the layer cannot serve as a reinforcing layer. On the other hand, when the thickness exceeds 50 µm, it becomes difficult to maintain the press-through property of the PEN film. PVC, PP, PET, PEN, and other materials are suitable as blister sheet materials from the viewpoint of transparency and moldability. Among them, PEN which constitutes also the cover material is most desired when recycling of the whole packaging material is taken into consideration. The blister sheet is required to have a capability of protecting the contents against external force and, further, moisture barrier properties enough to prevent ambient moisture from permeating into a pack, lightproofness enough to prevent the deterioration of the contents by light and, when the contents are foods, oxygen barrier properties. In particular, when moisture barrier properties are required, a sheet with PVDC being laminated thereto is suitable. The thickness of the blister sheet is, in many cases, about 100 to 500 µ m in a non-molded portion. The blister sheet, in which the contents are placed, is generally prepared by pressure forming or vacuum forming. If the blister is large, it may be prepared by plug-assist forming besides the above methods. Specifically, a plastic sheet is taken out from a spool, heated by means of a hot plate or an infrared heater and formed into a desired shape using a mold according to the shape of the contents. The easy-open package of the present invention is completed by bonding the stretched PEN film and the resin molding (blister, holding section) obtained above together by means of an adhesive or a heat seal. Roll sealing and flat sheet sealing may be mentioned as sealing methods. The roll sealing can realize stable filling and provide good appearance. Heat seal (HS) or contact bonding can be utilized for sealing between the blister and the cover (PEN film). Heat sealing agents include general heat sealing agents used for polyesters, which may be any of thermoplastic and thermosetting resins, such as nitrile rubber, urethane, chloroprene, epoxy, cyanoacrylate, and polyester resins. Although HS temperature may vary depending upon HS agents and the like, it is generally about 130 to 180°C. The HS agent may be of any of solvent, aqueous and hot-melt types, and isocyanate or other types of curing agents may, if necessary, be added thereto. The concentration of the isocyanate curing agent is suitably in the range of from 0.5 to 10 parts by weight based on 100 parts by weight, although it varies depending upon HS agents. When the concentration is less than 0.5 part by weight, the bonding strength cannot be enhanced. On the other hand, it exceeds 10 parts by weight, the HS layer becomes so hard that heat sealing becomes difficult. The HS agent may be laminated onto the stretched PEN film by coating or melt extrusion commonly used in the art. In the case of coating, gravure coating, three-roll coating, Komma coating, and other suitable coating methods are selected depending upon the HS agent. In the case of contact bonding, the pressure for this purpose is generally in the range of from about 1 to 10 kgf/cm 2 . The adhesive used in the contact bonding may be laminated onto the stretched PEN film by the same method as described above. As described above, the easy-open package of the present invention can be obtained by bonding the stretched PEN film and the resin molding (blister) obtained above together by means of an adhesive or a heat seal. Further, it is convenient to conduct blanking using a mold for the purpose of taking out necessary portions only or to provide perforations or slits so that the packs can be separated one by one. Furthermore, the provision of a printed layer by lamination followed by printing of inscriptions, such as name of contents, date of production, and expiration date for each pack enables the information to be confirmed, when the pack is separated and the contents thereof is taken, and, at the same time, can prevent erroneous taking of contents different from contemplated ones. Fig. 1 is a diagram showing a part of a stainless steel rod used in a press-through property test for a PEN resin film of the present invention. The present inventions will now be described respectively with reference to Example A. Example A The process for producing a PEN film and the PTP (press-through pack) according to the present invention will now be described in more detail with reference to the following examples. In the following examples, properties were measured by the following methods. Intrinsic viscosity: The intrinsic viscosity was determined by dissolving PEN resin in a solvent mixture of phenol and 1,1,2,2-tetrachloroethane (weight ratio = 6 : 4) at 100°C for 1 hr to a concentration in the range of from 0.2 to 1.0 g/dl, measuring the viscosity of the solution at 35°C with a Ubbelohde capillary viscometer and extrapolating the measured viscosity of the solution to 0 g/dl. Press-through property : A capsule (⊘6 x 15 mm) was packed into an article, produced by forming, in its holding portion and sealed with an adhesive. 24 hr after sealing, the capsule was pressed with a finger to observe whether or not the capsule can successfully break the cover material and come out therethrough, thereby evaluating the press-through property. Press-through strength and elongation : A stainless steel rod 1 (in a cylindrical form having a diameter of 9 mm with the end 2 being curved) having a mirror-finished end 2 as shown in Fig. 1 was descended perpendicularly to the film at a rate of 50 mm/min with the film being horizontally held to determine a strength and an elongation caused when the stainless steel rod is pressed through the film. These strength and elongation were regarded respectively as the press-through strength and press-through elongation. Combustibility : A cover material was heated from room temperature to 550°C at a temperature rise rate of 10°C/min in an air stream of 200 ml/min by means of TG/DTA 200 based on a thermal analysis system SSC 5000 manufactured by Seiko Instruments Inc. (thermogravimetry/differential thermal analyzer), and the residue was weighed to evaluate the combustibility. Gas permeability : The gas permeability was measured by means of a model GPM-250 gas permeability tester manufactured by G.L. Science Co., Ltd. at 23°C under atmospheric pressure by gas chromatography, using pure oxygen as a measuring gas. Transparency : The transparency of the cover material film was evaluated by visual inspection. Water vapor permeability : The water vapor permeability was measured by means of PERMATRAN-W6 type water-vapor measuring device manufactured by MOCON at 23°C under atmospheric pressure using dry N 2 as a carrier gas. Example A-1 A polyethylene-2,6-naphthalate polymer having an intrinsic viscosity of 0.41 with 0.1% by weight of kaolin having an average particle diameter of 0.3 µm being added thereto was prepared by polymerization. The polymer was dried at 150°C for 10 hr and melt-extruded at 290°C by means of a T-die extruder having a barrel diameter of 30⊘ to prepare an unstretched film (width: 220 µ m, thickness: 15 µm). The unstretched film was heat-treated at 210°C for 4 sec. A polyester thermoplastic adhesive was gravure-coated on a polyethylene-2,6-naphthalate film at a coverage of 8 g/m 2 . The coated film was used to heat-seal, at 160°C for 1 sec, a vacuum-formed product (a blister) of vinyl chloride into which a capsule has been packed, thereby preparing a PTP. The conditions for the preparation of the packaging material for a press-through pack are specified in Table A1, and the results of evaluation of the packaging material for a press-through pack are given in Table A2. The packaging material for a press-through pack had excellent press-through property, combustibility, and transparency. Examples A-2 to A-5 and Reference Example AR-1 The procedure of Example A-1 was repeated, except that the polymerization time was varied to vary the intrinsic viscosity of polyethylene-2,6-naphthalate polymer. The conditions for the preparation of the packaging materials for a press-through pack are specified in Table A1, and the results of evaluation of the packaging materials for a press-through pack are given in Table A2. Examples A-6 to A-9 and Reference Example AR-2 The procedure of Example A-1 was repeated, except that the thickness of the polyethylene-2,6-naphthalate film was varied. The conditions for the preparation of the packaging materials for a press-through pack are specified in Table A1, and the results of evaluation of the packaging materials for a press-through pack are given in Table A2. Examples A-10 to A-13 The procedure of Example A-1 was repeated, except that the thickness of the unstretched film was 30 µm and, after extrusion, the unstretched film was stretched at 140 to 270°C in longitudinal and transverse directions and then heat-treated at 210°C for 4 sec to prepare a 15 µm-thick film. The conditions for the preparation of the packaging material for a press-through pack are specified in Table A1, and the results of evaluation of the packaging material for a press-through pack are given in Table A2. Examples A-14 to A-18 and Reference Example AR-3 The procedure of Example A-1 was repeated, except that the thickness of the unstretched film was varied and, after extrusion, the unstretched film was stretched at 135°C in longitudinal and transverse directions and then heat-treated at 210°C for 4 sec to prepare a 15 µ m-thick film. The conditions for the preparation of the packaging materials for a press-through pack are specified in Table A1, and the results of evaluation of the packaging materials for a press-through pack are given in Table A2. Examples A-19 to A-23 and Reference Example AR-4 and AR-5 The procedure of Example A-1 was repeated, except that the heat setting conditions (temperature or time) were varied. The conditions for the preparation of the packaging materials for a press-through pack are specified in Table A1, and the results of evaluation of the packaging materials for a press-through pack are given in Table A2. Examples A-24 to A-27 The procedure of Example A-1 was repeated, except that the material for a vacuum-formed product of the resin in the packaging material for a press-through pack was varied. The conditions for the preparation of the packaging materials for a press-through pack are specified in Table A1, and the results of evaluation of the packaging materials for a press-through pack are given in Table A2. Examples A-28 The procedure of Example A-1 was repeated, except that an inflation extruder having a width of ⊘50 mm was used as the extruder with the die temperature being 290°C. The conditions for the preparation of the packaging materials for a press-through pack are specified in Table A1, and the results of evaluation of the packaging materials for a press-through pack are given in Table A2. Examples A-29 to A-30 The procedure of Example A-28 was repeated, except that the blow ratio and the stretch ratio in the take-up direction were 1.5 to 2.5 times. The conditions for the preparation of the packaging materials for a press-through pack are specified in Table A1, and the results of evaluation of the packaging materials for a press-through pack are given in Table A2. Comparative Examples AC-1 to AC-4 The procedure of Example A-1 was repeated, except that the cover material for a press-through pack was varied. The stretching conditions for PP and PET were those suitable for the respective materials. The conditions for the preparation of the packaging materials for a press-through pack are specified in Table A1, and the results of evaluation of the packaging materials for a press-through pack are given in Table A2. Conditions for preparation of packaging material for press-through pack In- trinsic viscosity of PEN Thick- ness [µm] Stretch- ing temp. [°C] Stretch ratio Heat setting Vacuum forming Longitudinal Transverse Temp. [°C] Time [s] A-1 0.41 15 - - 210 4 Vinyl chloride A-2 0.31 15 - - 210 4 Vinyl chloride A-3 0.36 15 - - 210 4 Vinyl chloride A-4 0.47 15 - - 210 4 Vinyl chloride A-5 0.59 15 - - 210 20 Vinyl chloride A-6 0.41 10 - - 210 4 Vinyl chloride A-7 0.41 30 - - 210 4 Vinyl chloride A-8 0.41 45 - - 210 4 Vinyl chloride A-9 0.36 150 - - 210 10 min Vinyl chloride A-10 0.41 15 140 1.5 1.5 210 4 Vinyl chloride A-11 0.41 15 160 1.5 1.5 210 4 Vinyl chloride A-12 0.41 15 220 1.5 1.5 210 4 Vinyl chloride A-13 0.41 15 270 1.5 1.5 210 4 Vinyl chloride A-14 0.41 15 135 1.0 1.5 210 4 Vinyl chloride A-15 0.41 15 135 1.0 2.7 210 4 Vinyl chloride A-16 0.41 15 135 1.5 1.5 210 4 Vinyl chloride A-17 0.41 15 135 1.5 2.7 210 4 Vinyl chloride A-18 0.41 15 135 2.7 2.7 210 4 Vinyl chloride A-19 0.41 15 - - 180 30 min Vinyl chloride A-20 0.41 15 - - 210 1 Vinyl chloride A-21 0.41 15 - - 210 4 Vinyl chloride A-22 0.41 15 - - 210 30 Vinyl chloride A-23 0.41 15 - - 250 60 Vinyl chloride A-24 0.41 15 - - 210 4 PEN A-25 0.41 15 - - 210 4 PP A-26 0.41 15 - - 210 4 PET A-27 0.41 15 - - 210 4 COC A-28 0.41 15 - - 210 4 Vinyl chloride A-29 0.41 15 260 1.5 1.5 210 4 Vinyl chloride A-30 0.41 15 260 2.5 2.5 210 4 Vinyl chloride AR-1 0.62 15 - - 210 30 Vinyl chloride AR-2 0.41 200 - - 210 30 Vinyl chloride AR-3 0.41 15 135 3.5 3.5 210 4 Vinyl chloride AR-4 0.41 15 - - - - Vinyl chloride AR-5 0.41 15 - - 160 30 Vinyl chloride AC-1 Glassine paper 15 - - - - Vinyl chloride AC-2 Aluminum foil 20 - - - - Vinyl chloride AC-3 PET 15 - - 190 10 Vinyl chloride AC-4 PP 15 - - 170 10 Vinyl chloride Results of evaluation of packaging material for press through pack Pressthrough property Combustibility Transparency Press-through of film Strength [kgf] Elongation [mm] A-1 1.3 2 A-2 1.2 2 A-3 1.2 2 A-4 1.3 2 A-5 1.6 2 A-6 1.1 2 A-7 1.5 2 A-8 1.7 3 A-9 4.2 6 A-10 1.6 3 A-11 1.5 2 A-12 1.5 2 A-13 1.4 2 A-14 1.6 2 A-15 2.1 3 A-16 2.0 3 A-17 2.1 4 A-18 2.2 4 A-19 1.3 2 A-20 1.3 2 A-21 1.3 2 A-22 1.2 2 A-23 1.2 2 A-24 1.3 2 A-25 1.3 2 A-26 1.3 2 A-27 1.3 2 A-28 1.3 2 A-29 1.4 2 A-30 1.6 3 AR-1 2.2 17 AR-2 7.9 27 AR-3 3.0 33 AR-4 1.4 40 AR-5 1.4 23 AC-1 1.9 2 AC-2 1.5 2 AC-3 4.2 21 AC-4 3.7 20 Examples A-31 to A-37 Unstretched films were prepared by molding in the same manner as in Example A-1, except that polypropylene (PP) or polyethylene (PE) or nylon (Ny) was co-extruded. Packaging materials for PTP were prepared in the same manner as in Example A-1, except that the above unstretched films were used. Thereafter, the PP or PE or Ny layer was removed, and the packaging materials were then evaluated in the same manner as in Example A-1. The constructions of the packaging materials before the removal of the PP or PE or Ny layer are shown in Table A3, the conditions for the preparation of the packaging materials for PTP are specified in Table A4, and the results of evaluation of the packaging materials for PTP after the removal of the PP or PE or Ny layer are given in Table A5. The packaging materials for a press-through pack had excellent press-through property, combustibility, and transparency. Examples A-38 to A-40 Unstretched films were prepared by molding in the same manner as in Example A-28, except that polypropylene (PP) or polyethylene (PE) or nylon (Ny) was co-extruded. Packaging materials for PTP were prepared in the same manner as in Example A-28, except that the above unstretched films were used. Thereafter, the PP or PE or Ny layer was removed, and the packaging materials were then evaluated in the same manner as in Example A-28. The constructions of the packaging materials before the removal of the PP or PE or Ny layer are shown in Table A3, the conditions for the preparation of the packaging materials for PTP are specified in Table A4, and the results of evaluation of the packaging materials for PTP after the removal of the PP or PE or Ny layer are given in Table A5. The packaging materials for a press-through pack had excellent press-through property, combustibility, and transparency. Construction before removing olefin layer and film forming method Construction Film forming method A-31 PEN (15)/PP (10) T-die co-extrusion A-32 PEN (15)/PP (20) T-die co-extrusion A-33 PEN (15)/PE (10) T-die co-extrusion A-34 PEN (15)/PE (20) T-die co-extrusion A-35 PEN (15)/Ny (10) T-die co-extrusion A-36 PEN (15)/Ny (20) T-die co-extrusion A-37 PEN (20)/PP (20) T-die co-extrusion A-38 PEN (15)/PP (20) Inflation co-extrusion A-39 PEN (15)/PE (20) Inflation co-extrusion A-40 PEN (15)/Ny (20) Inflation co-extrusion Conditions for preparation of packaging material for PTP Intrinsic viscosity of PEN Thickness [µm] Stretching temp. [°C] Stretch ratio Heat setting Vacuum forming Longitudinal Transverse Temp. [°C] Time [s] A-31 0.41 15 The same as A-1 210 4 Vinyl chloride A-32 0.41 15 The same as A-1 210 4 Vinyl chloride A-33 0.41 15 The same as A-1 210 4 Vinyl chloride A-34 0.41 15 The same as A-1 210 4 Vinyl chloride A-35 0.41 15 The same as A-1 210 4 Vinyl chloride A-36 0.41 15 The same as A-1 210 4 Vinyl chloride A-37 0.41 15 The same as A-1 210 4 Vinyl chloride A-38 0.41 15 The same as A-28 210 4 Vinyl chloride A-39 0.41 15 The same as A-28 210 4 Vinyl chloride A-40 0.41 15 The same as A-28 210 4 Vinyl chloride Results of evaluation of packaging material for press-through pack Press-through property Combustibility Transparency Press-through of film Strength [kgf] Elongation [mm] A-31 ○ ○ ○ 1.3 2 A-32 ○ ○ ○ 1.3 2 A-33 ○ ○ ○ 1.3 2 A-34 ○ ○ ○ 1.3 2 A-35 ○ ○ ○ 1.3 2 A-36 ○ ○ ○ 1.3 2 A-37 ○ ○ ○ 1.3 2 A-38 ○ ○ ○ 1.3 2 A-39 ○ ○ ○ 1.3 2 A-40 ○ ○ ○ 1.3 2 Examples A-41 to A-52 In Examples A-41 to A-52, the procedure of Example A-1 or Example A-28 was repeated, except that a water-vapor barrier resin was laminated to the polyethylene-2,6-naphthalate film and vinyl chloride (PVC) to be vacuum-formed was coated with vinylidene chloride (PVDC). The lamination was carried out by extrusion coating (EC, heat lamination) for Examples A-41 to A-43, T-die co-extrusion for Examples A-44 to A-46, inflation co-extrusion for Examples A-47 to A-49, coating for Example A-50, and vapor deposition for Examples A-51 and A-52. The adhesive used was a polyester AC agent for EC and a modified polyester adhesive resin for the T-die co-extrusion and the inflation co-extrusion. The constructions and the water vapor permeability of the PEN films with water vapor barrier resins being laminated thereto are given in Table A6. The conditions for the preparation of the packaging materials for PTP are specified in Table A7, and the results of evaluation of the packaging materials for PTP are given in Table A8. The PTP's using the packaging materials prepared in Examples A-41 to A-52 and the PTP using the packaging material prepared in Example A-1 were allowed to stand in an atmosphere kept at 25°C and 90%RH for 30 days. As a result, no moisture absorption was observed for the contents of the PTP's using the packaging materials prepared in Examples A-41 to A-52, whereas moisture absorption was observed for contents of the PTP using the packaging material prepared in Example A-1. Construction and water vapor permeability of PEN film with water vapor barrier resin being laminated thereto Construction Water vapor permeability Laminating method [g/m 2 ·24hr] A-41 PEN(15)/AD(2)/PE(13) 30 EC A-42 PEN(15)/AD(2)/PP(13) 20 EC A-43 PEN(15)/AD(2)/COC(13) 12 EC A-44 PEN(15)/AD(2)/PE(13) 30 T-die co-extrusion A-45 PEN(15)/AD(2)/PP(13) 20 T-die co-extrusion A-46 PEN(15)/AD(2)/COC(13) 12 T-die co-extrusion A-47 PEN(15)/AD(2)/PE(13) 30 Inflation co-extrusion A-48 PEN(15)/AD(2)/PP(13) 20 Inflation co-extrusion A-49 PEN(15)/AD(2)/COC(13) 12 Inflation co-extrusion A-50 PEN(15)/PVCD(5) 5 Coating A-51 PEN(15)/SiO x (200A) Not more than 0.5 Vapor deposition A-52 PEN(15)/Al 2 O 3 (1500A) 3 Vapor deposition Note: Value within (): thickness [µm] A: angstrom AD: adhesive layer Conditions for preparation of packaging material for PTP Intrinsic viscosity of PEN Thickness [µm] Stretching temp. [°C] Stretch ratio Heat setting Vacuum forming Longitudinal Transverse Temp. [°C] Time [s] A-41 0.41 30 - - 210 4 Vinyl chloride A-42 0.41 30 - - 210 4 Vinyl chloride A-43 0.41 30 - - 210 4 Vinyl chloride A-44 0.41 30 The same as A-1 210 4 Vinyl chloride A-45 0.41 30 The same as A-1 210 4 Vinyl chloride A-46 0.41 30 The same as A-1 210 4 Vinyl chloride A-47 0.41 30 The same as A-28 210 4 Vinyl chloride A-48 0.41 30 The same as A-28 210 4 Vinyl chloride A-49 0.41 30 The same as A-28 210 4 Vinyl chloride A-50 0.41 20 - - 210 4 Vinyl chloride A-51 0.41 15 - - 210 4 Vinyl chloride A-52 0.41 15 - - 210 4 Vinyl chloride Results of evaluation of packaging material for press-through pack Press-through property Combustibility Transparency Press-through of film Strength [kgf] Elongation [mm] A-41 ○ ○ ○ 1.4 3 A-42 ○ ○ ○ 1.4 3 A-43 ○ ○ ○ 1.4 3 A-44 ○ ○ ○ 1.4 3 A-45 ○ ○ ○ 1.4 3 A-46 ○ ○ ○ 1.4 3 A-47 ○ ○ ○ 1.4 3 A-48 ○ ○ ○ 1.4 3 A-49 ○ ○ ○ 1.4 3 A-50 ○ ○ ○ 1.3 3 A-51 ○ ○ ○ 1.3 2 A-52 ○ ○ ○ 1.3 2 Examples A-53 to A-59 In Example A-53 to A-59, the procedure of Example A-1 or Example A-28 was repeated, except that an oxygen barrier resin was laminated to the polyethylene-2,6-naphthalate film, vinyl chloride (PVC) to be vacuum-formed was coated with vinylidene chloride (PVDC), and the contents of the pack were solid fats and oils. The lamination was carried out by T-die co-extrusion for Examples A-53 to A-54, inflation co-extrusion for Examples A-55 and A-56, coating for Example A-57, and vapor deposition for Examples A-58 and A-59. The adhesive layer comprised a modified polyester adhesive resin for Examples A-53 to A-56. The constructions and the oxygen permeability of the PEN films with oxygen barrier resins being laminated thereto are given in Table A9. The conditions for the preparation of the packaging materials for PTP are specified in Table A10, and the results of evaluation of the packaging materials for PTP are given in Table A11. The PTP's using the packaging materials prepared in Examples A-53 to A-59, and the PTP using the packaging material prepared in Example A-1 were allowed to stand in an atmosphere kept at 25°C and 90%RH for 30 days. As a result, it was found that the contents of the PTP's using the packaging materials prepared in Examples A-53 to A-59 were not oxidized, whereas the contents of the packaging material prepared in Example A-1 were oxidized. Construction and oxygen permeability of PEN film with oxygen barrier resin being laminated thereto Construction Oxygen permeability Laminating method [g/m 2 ·24hr] A-53 PEN(15)/AD(2)/PVA(13) 4 T-die co-extrusion A-54 PEN(10)/AD(2)/EVOH(5) /AD(2)/PEN(10) 10 T-die co-extrusion A-55 PEN(15)/AD(2)/PVA(13) 4 Inflation co-extrusion A-56 PEN(10)/AD(2)/EVOH(5) /AD(2)/PEN(10) 10 Inflation co-extrusion A-57 PEN(15)/PVDC(5) 5 Coating A-58 PEN(15)/SiO x (200A) Not more than 0.5 Vapor deposition A-59 PEN(15)/Al 2 O 3 (1500A) 3 Vapor deposition Conditions for preparation of packaging material for PTP Intrinsic viscosity of PEN Thickness [µm] Stretching temp. [°C] Stretch ratio Heat setting Vacuum forming Longitudinal Transverse Temp. [°C] Time [s] A-53 0.41 30 The same as A-1 210 4 Vinyl chloride A-54 0.41 29 The same as A-1 210 4 Vinyl chloride A-55 0.41 30 The same as A-28 210 4 Vinyl chloride A-56 0.41 29 The same as A-28 210 4 Vinyl chloride A-57 0.41 20 - - 210 4 Vinyl chloride A-58 0.41 15 - - 210 4 Vinyl chloride A-59 0.41 15 - - 210 4 Vinyl chloride Results of evaluation of packaging material for press-through pack Press-through property Combustibility Transparency Press-through of film Strength [kgf] Elongation [mm] A-53 ○ ○ ○ 1.4 3 A-54 ○ ○ ○ 1.5 3 A-55 ○ ○ ○ 1.4 3 A-56 ○ ○ ○ 1.5 3 A-57 ○ ○ ○ 1.3 3 A-58 ○ ○ ○ 1.3 2 A-59 ○ ○ ○ 1.3 2 Examples A-60 to A-65 In Examples A-60 to A-65, the procedure of Example A-1 or Example A-28 was repeated, except that a water-vapor barrier resin and an oxygen barrier resin were laminated to the polyethylene-2,6-naphthalate film and vinyl chloride (PVC) to be vacuum-formed was coated with vinylidene chloride (PVDC). The lamination was carried out by T-die co-extrusion for Examples A-60 to A-62 and inflation co-extrusion for Examples A-63 and A-65. The adhesive layer comprised a modified polyester adhesive resin. The constructions, the water vapor permeability, and the oxygen permeability of the PEN films with water-vapor barrier resins and oxygen barrier resins being laminated thereto are given in Table A12. The conditions for the preparation of the packaging materials for PTP are specified in Table A13, and the results of evaluation of the packaging materials for PTP are given in Table A14. The PTP's using the packaging materials prepared in Examples A-60 to A-65, and the PTP using the packaging material prepared in Example A-1 were allowed to stand in an atmosphere kept at 25°C and 90%RH for 30 days. As a result, no moisture absorption was observed for the contents of the PTP's using the packaging materials prepared in Examples A-60 to A-65, whereas moisture absorption was observed for the contents of the PTP using the packaging material prepared in Example A-1. Construction, water vapor permeability and oxygen permeability of PEN film with water vapor barrier layer and oxygen barrier resin being laminated thereto Construction Water vapor permeability [g/m 2 ·24hr] Oxygen permeability [g/m 2 ·24hr] Laminating method A-60 PEN(10)/AD(2)/ EVOH(5)/AD(2)/ PE(10) 35 10 T-die co-extrusion A-61 PEN(10)/AD(2)/ EVOH(5)/AD(2)/ COC(5) 7 10 T-die co-extrusion A-62 PEN(10)/AD(2)/ PVA(10)/AD(2)/ PP(10) 15 5 T-die co-extrusion A-63 PEN(10)/AD(2)/ EVOH(5)/AD(2)/ PE(10) 35 10 Inflation co-extrusion A-64 PEN(10)/AD(2)/ EVOH(5)/AD(2)/ COC(5) 7 10 Inflation co-extrusion A-65 PEN(10)/AD(2)/ PVA(10)/AD(2)/ PP(10) 15 5 Inflation co-extrusion Conditions for preparation of packaging material for PTP Intrinsic viscosity of PEN Thickness [µm] Stretching temp. [°C] Stretch ratio Heat setting Vacuum forming Longitudinal Transverse Temp. [°C] Time [s] A-60 0.41 31 The same as A-1 210 4 Vinyl chloride A-61 0.41 24 The same as A-1 210 4 Vinyl chloride A-62 0.41 34 The same as A-1 210 4 Vinyl chloride A-63 0.41 31 The same as A-28 210 4 Vinyl chloride A-64 0.41 24 The same as A-28 210 4 Vinyl chloride A-65 0.41 34 The same as A-28 210 4 Vinyl chloride Results of evaluation of packaging material for press-through pack Press-through property Combustibility Transparency Press-through of film Strength [kgf] Elongation [mm] A-60 ○ ○ ○ 1.4 4 A-61 ○ ○ ○ 1.4 2 A-62 ○ ○ ○ 1.5 3 A-63 ○ ○ ○ 1.4 4 A-64 ○ ○ ○ 1.4 2 A-65 ○ ○ ○ 1.5 3 Examples A-66 to A-83 The procedure of Example A-1 or Example A-28 was repeated, except that a reinforcing layer of a synthetic resin was laminated to the polyethylene-2,6-naphthalate film prepared in Example A-1 or Example A-28. The lamination was carried out by EC for Examples A-66 to A-71, T-die co-extrusion for Examples A-72 to A-77, and inflation co-extrusion for Examples A-78 to A-83. The adhesive layer comprised a modified polyester AC agent for EC and a modified polyester adhesive resin for the T-die co-extrusion and the inflation co-extrusion. The constructions of the PEN films with reinforcing layers being laminated thereto are given in Table A15. The conditions for the preparation of the packaging materials for PTP are specified in Table A16, and the results of evaluation of the packaging materials for PTP are given in Table A17. Construction of PEN film with reinforcing layer laminated thereto Construction Laminating method A-66 PEN(8)/AD(2)/PE(10) EC A-67 PEN(15)/AD(2)/PE(20) EC A-68 PEN(8)/AD(2)/PP(10) EC A-69 PEN(15)/AD(2)/PP(20) EC A-70 PEN(8)/AD(2)/COC(10) EC A-71 PEN(15)/AD(2)/COC(20) EC A-72 PEN(8)/AD(2)/PE(10) T-die co-extrusion A-73 PEN(15)/AD(2)/PE(20) T-die co-extrusion A-74 PEN(8)/AD(2)/PP(10) T-die co-extrusion A-75 PEN(15)/AD(2)/PP(20) T-die co-extrusion A-76 PEN(8)/AD(2)/COC(10) T-die co-extrusion A-77 PEN(15)/AD(2)/COC(20) T-die co-extrusion A-78 PEN(8)/AD(2)/PE(10) Inflation co-extrusion A-79 PEN(15)/AD(2)/PE(20) Inflation co-extrusion A-80 PEN(8)/AD(2)/PP(10) Inflation co-extrusion A-81 PEN(15)/AD(2)/PP(20) Inflation co-extrusion A-82 PEN(8)/AD(2)/COC(10) Inflation co-extrusion A-83 PEN(15)/AD(2)/COC(20) Inflation co-extrusion Conditions for preparation of packaging material for PTP Intrinsic viscosity of PEN Thickness [µm] Stretching temp. [°C] Stretch ratio Heat setting Vacuum forming Longitudinal Transverse Temp. [°C] Time [s] A-66 0.41 20 - - 210 4 Vinyl chloride A-67 0.41 37 - - 210 4 Vinyl chloride A-68 0.41 20 - - 210 4 Vinyl chloride A-69 0.41 37 - - 210 4 Vinyl chloride A-70 0.41 20 - - 210 4 Vinyl chloride A-71 0.41 37 - - 210 4 Vinyl chloride A-72 0.41 20 The same as A-1 210 4 Vinyl chloride A-73 0.41 37 The same as A-1 210 4 Vinyl chloride A-74 0.41 20 The same as A-1 210 4 Vinyl chloride A-75 0.41 37 The same as A-1 210 4 Vinyl chloride A-76 0.41 20 The same as A-1 210 4 Vinyl chloride A-77 0.41 37 The same as A-1 210 4 Vinyl chloride A-78 0.41 20 The same as A-28 210 4 Vinyl chloride A-79 0.41 37 The same as A-28 210 4 Vinyl chloride A-80 0.41 20 The same as A-28 210 4 Vinyl chloride A-81 0.41 37 The same as A-28 210 4 Vinyl chloride A-82 0.41 20 The same as A-28 210 4 Vinyl chloride A-83 0.41 37 The same as A-28 210 4 Vinyl chloride Results of evaluation of packaging material for press-through pack Press-through property Combustibility Transparency Press-through of film Strength [kgf] Elongation [mm] A-66 ○ ○ ○ 1.2 3 A-67 ○ ○ ○ 1.4 3 A-68 ○ ○ ○ 1.3 3 A-69 ○ ○ ○ 1.4 3 A-70 ○ ○ ○ 1.3 2 A-71 ○ ○ ○ 1.4 2 A-72 ○ ○ ○ 1.2 3 A-73 ○ ○ ○ 1.4 3 A-74 ○ ○ ○ 1.3 3 A-75 ○ ○ ○ 1.4 3 A-76 ○ ○ ○ 1.3 2 A-77 ○ ○ ○ 1.4 2 A-78 ○ ○ ○ 1.2 3 A-79 ○ ○ ○ 1.4 3 A-80 ○ ○ ○ 1.3 3 A-81 ○ ○ ○ 1.4 3 A-82 ○ ○ ○ 1.3 2 A-83 ○ ○ ○ 1.4 2 Examples A-84 to A-91 In Examples A-84 to A-91, the procedure of Example A-1 or Example A-28 was repeated, except that a water-vapor barrier resin and/or an oxygen barrier resin were laminated to the polyethylene-2,6-naphthalate film, a reinforcing layer was laminated thereto, vinyl chloride (PVC) to be vacuum-formed was coated with vinylidene chloride (PVDC) and the contents were a hygroscopic chemical. The lamination was carried out by T-die co-extrusion for Examples A-84 to A-87 and inflation co-extrusion for Examples A-88 and A-91. The adhesive layer comprised a modified polyester adhesive resin. The constructions, the water vapor permeability, and the oxygen permeability of PEN films with a water vapor barrier resin and/or an oxygen barrier resin and a reinforcing layer being laminated thereto are given in Table A18. The conditions for the preparation of the packaging materials for PTP are specified in Table A19, and the results of evaluation of the packaging materials for PTP are given in Table A20. The PTP's using the packaging materials prepared in Examples A-84 to A-91, and the PTP using the packaging material prepared in Example A-1 were allowed to stand in an atmosphere kept at 25°C and 90%RH for 30 days. As a result, no moisture absorption was observed for the contents of the PTP's using the packaging materials prepared in Examples A-84 to A-91, whereas moisture absorption was observed for the contents of the PTP using the packaging material prepared in Example A-1. Construction of PEN film with water vapor barrier layer or oxygen barrier layer or both vapor barrier layer and reinforcing layer laminated thereto Construction Water vapor permeability [g/m 2 ·24hr] Oxygen permeability [g/m 2 ·24hr] Laminating method A-84 PEN(10)/AD(2)/ EVOH(5)/AD(2)/ PE(15) 22 10 T-die co-extrusion A-85 PEN(10)/AD(2)/ EVOH(5)/AD(2)/ PP(15) 15 10 T-die co-extrusion A-86 PEN(10)/AD(2)/ PVA(10)/AD(2)/ COC(0)/AD(2)/ PP(10) 10 5 T-die co-extrusion A-87 PEN(10)/AD(2)/ PVA(10)/AD(2)/ COC(10)/AD(2)/ Ny(10) 10 5 T-die co-extrusion A-88 PEN(10)/AD(2)/ EVOH(5)/AD(2)/ PE(15) 22 10 Inflation co-extrusion A-89 PEN(10)/AD(2)/ EVOH(5)/AD(2)/ PP(15) 15 10 Inflation co-extrusion A-90 PEN(10)/AD(2)/ PVA(10)/AD(2)/ COC(10)/AD(2)/ PP(10) 10 5 Inflation co-extrusion A-91 PEN(10)/AD(2)/ PVA(10)/AD(2)/ COC(10)/AD(2)/ Ny(10) 10 5 Inflation co-extrusion Conditions for preparation of packaging material for PTP Intrinsic viscosity of PEN Thickness [µm] Stretching temp. [°C] Stretch ratio Heat setting Vacuum forming Longitudinal Transverse Temp. [°C] Time [s] A-84 0.41 34 The same as A-1 210 4 Vinyl chloride A-85 0.41 34 The same as A-1 210 4 Vinyl chloride A-86 0.41 46 The same as A-1 210 4 Vinyl chloride A-87 0.41 46 The same as A-1 210 4 Vinyl chloride A-88 0.41 34 The same as A-28 210 4 Vinyl chloride A-89 0.41 34 The same as A-28 210 4 Vinyl chloride A-90 0.41 46 The same as A-28 210 4 Vinyl chloride A-91 0.41 46 The same as A-28 210 4 Vinyl chloride Results of evaluation of packaging material for press-through pack Press-through property Combustibility Transparency Press-through of film Strength [kgf] Elongation [mm] A-84 ○ ○ ○ 1.4 4 A-85 ○ ○ ○ 1.5 3 A-86 ○ ○ ○ 1.5 4 A-87 ○ ○ ○ 1.6 4 A-88 ○ ○ ○ 1.4 4 A-89 ○ ○ ○ 1.5 3 A-90 ○ ○ ○ 1.5 4 A-91 ○ ○ ○ 1.6 4 Examples A-92 to A-97 In Examples A-92 and A-97 and Reference Example AR-6, the procedure of Examples A-1, A-79, A-81 and A-83 and Reference Example AR-2 was repeated, except that the film thickness was varied, the contents were a working cutter (length: 150 mm) and a vacuum-formed product for a working cutter was used. The conditions for the preparation of the packaging materials for PTP are specified in Table A21, and the results of evaluation of the packaging materials for PTP are given in Table A22. For the packaging material of PTP in Reference Example AR-6, it was difficult to take out the contents from PTP. Conditions for preparation of packaging material for PTP Intrinsic viscosity of PEN Thickness [µm] Stretching temp. [°C] Stretch ratio Heat setting Vacuum forming Longitudinal Transverse Temp. [°C] Time [s] A-92 0.41 20 The same as A-1 210 4 Vinyl chloride A-93 0.41 45 The same as A-1 210 4 Vinyl chloride A-94 0.41 150 The same as A-1 210 4 Vinyl chloride A-95 0.41 37 The same as A-79 210 4 Vinyl chloride A-96 0.41 37 The same as A-81 210 4 Vinyl chloride A-97 0.41 37 The same as A-83 210 4 Vinyl chloride AR-6 0.41 200 The same as AR-2 210 30 Vinyl chloride Results of evaluation of packaging material for press-through pack Press-through property Combustibility Transparency A-92 ○ ○ ○ A-93 ○ ○ ○ A-94 ○ ○ ○ A-95 ○ ○ ○ A-96 ○ ○ ○ A-97 ○ ○ ○ AR-6 X ○ ○ Examples A-98 to A-103 In Examples A-98 to A-103 and Reference Example AR-7, the procedure of Examples A-1, A-28, A-29, A-79, A-81 and A-83 and Reference Example AR-2 was repeated, except that the contents were a toothbrush for interdentium (approximate dimension: ⊘8 x 45 mm) and the vacuum-formed product was one for a toothbrush for interdentium. The conditions for the preparation of the packaging materials for PTP are specified in Table A23, and the results of evaluation of the packaging materials for PTP are given in Table A24. The packaging material for PTP in Reference Example AR-7, it was difficult to take out the contents from PTP. Conditions for preparation of packaging material for PTP Intrinsic viscosity of PEN Thickness [µm] Stretching temp. [°C] Stretch ratio Heat setting Vacuum forming Longitudinal Transverse Temp. [°C] Time [s] A-98 0.41 15 The same as A-1 210 4 Vinyl chloride A-99 0.41 15 The same as A-28 210 4 Vinyl chloride A-100 0.41 15 The same as A-29 210 4 Vinyl chloride A-101 0.41 37 The same as A-79 210 4 Vinyl chloride A-102 0.41 37 The same as A-81 210 4 Vinyl chloride A-103 0.41 37 The same as A-83 210 4 Vinyl chloride AR-7 0.41 200 The same as AR-2 210 30 Vinyl chloride Results of evaluation of packaging material for press-through pack Press-through property Combustibility Transparency A-98 ○ ○ ○ A-99 ○ ○ ○ A-100 ○ ○ ○ A-101 ○ ○ ○ A-102 ○ ○ ○ A-103 ○ ○ ○ AR-7 X ○ ○ Examples A-104 to A-109 In Examples A-104 to A-109, the PEN films prepared in Examples A-1, A-28, A-29, A-48, A-49 and A-50 were subjected to sealing to form bags having a size of 30 x 30 mm, and a powdered drug (100 mg) was used as the contents. The conditions for the preparation of the packaging materials are specified in Table A25, and the results of evaluation are given in Table A26. The packaging materials had excellent easy tear property, combustibility, and transparency. The PTP's using the packaging materials prepared in Examples A-107, A-108, and A-109 were allowed to stand in an atmosphere kept at 25°C and 90%RH for 30 days. As a result, the contents did not absorb any moisture. Conditions for preparation of packaging material Intrinsic viscosity of PEN Thickness [µm] Stretching temp. [°C] Stretch ratio Heat setting Vacuum forming Longitudinal Transverse Temp. [°C] Time [s] A-104 0.41 15 The same as A-1 210 4 Vinyl chloride A-105 0.41 15 The same as A-28 210 4 Vinyl chloride A-106 0.41 15 The same as A-29 210 4 Vinyl chloride A-107 0.41 30 The same as A-48 210 4 Vinyl chloride A-108 0.41 30 The same as A-49 210 4 Vinyl chloride A-109 0.41 20 The same as A-50 210 4 Vinyl chloride Results of evaluation of packaging material Easy tearing Combustibility Transparency A-104 ○ ○ ○ A-105 ○ ○ ○ A-106 ○ ○ ○ A-107 ○ ○ ○ A-108 ○ ○ ○ A-109 ○ ○ ○ Examples A-110 to A-115 In Examples A-110 to A-115, the PEN films prepared in Examples A-1, A-28, A-29, A-48, A-60 and A-81 were used as a cover material for a paper milk pack (capacity: 200 ml) in its opening through which a straw is to be pierced. The conditions for the preparation of the cover material are specified in Table A27, and the results of evaluation are given in Table A28. In Examples A-113 to A-115, an isocyanate AC agent was coated at a coverage of 0.5 g/m on the side of PP or PE, and a polyester adhesive was then coated thereon to form a bonding face. The packaging materials thus prepared had sufficient strength to be used as a cover material, and a straw could be easily pierced through the packaging materials to make a hole (easy piercing). Further, they had excellent combustibility and transparency. Conditions for preparation of cover material Intrinsic viscosity of PEN Thickness [µm] Stretching temp. [°C] Stretch ratio Heat setting Vacuum forming Longitudinal Transverse Temp. [°C] Time [s] A-110 0.41 15 The same as A-1 210 4 Vinyl chloride A-111 0.41 15 The same as A-28 210 4 Vinyl chloride A-112 0.41 15 The same as A-29 210 4 Vinyl chloride A-113 0.41 30 The same as A-48 210 4 Vinyl chloride A-114 0.41 31 The same as A-60 210 4 Vinyl chloride A-115 0.41 37 The same as A-81 210 4 Vinyl chloride Results of evaluation of cover material Easy piecing Combustibility Transparency A-110 ○ ○ ○ A-111 ○ ○ ○ A-112 ○ ○ ○ A-113 ○ ○ ○ A-114 ○ ○ ○ A-115 ○ ○ ○ Examples A-116 to A-118 In Examples A-116 to A-118, the procedure of Examples A-65, A-75 and A-83 was repeated, except that an isocyanate AC agent was coated at a coverage of 0.5 g/m on the PP, PE or COC surface of the PEN films and a polyester adhesive was coated thereon to form a bonding face. The conditions for the preparation of the packaging materials for a press-through pack are specified in Table A29, and the results of evaluation of the packaging materials for a press-through pack are given in Table A30. The packaging materials for a press-through pack had excellent press-through property, combustibility, and transparency. Conditions for preparation of packaging material for PTP Intrinsic viscosity of PEN Thickness [µm] Stretching temp. [°C] Stretch ratio Heat setting Vacuum forming Longitudinal Transverse Temp. [°C] Time [s] A-116 0.41 37 The same as A-65 210 4 Vinyl chloride A-117 0.41 20 The same as A-75 210 4 Vinyl chloride A-118 0.41 37 The same as A-83 210 4 Vinyl chloride Results of evaluation of packaging material for press-through pack Press-through property Combustibility Transparency Press-through of film Strength [kgf] Elongation [mm] A-116 ○ ○ ○ 1.4 3 A-117 ○ ○ ○ 1.3 2 A-118 ○ ○ ○ 1.4 3 Example A' Further, the process for producing a PEN film having stretch ratios of 3 to 6 times and 1 to 1.8 times respectively in substantially mutually perpendicularly directions and PTP's (press-through packs) according to the present invention will now be described in more detail with reference to the following examples. The properties in each example were measured in the same manner as in Example A. Example A'-1: A polyethylene-2,6-naphthalate polymer having an intrinsic viscosity of 0.41 with 0.1% by weight of kaolin having an average particle diameter of 0.3 µ m being added thereto was prepared by polymerization. The polymer was dried at 140°C for 10 hr and melt-extruded at 290°C by means of a T-die extruder having a barrel diameter of 30⊘ to prepare an unstretched film (width: 220 mm, thickness: 80 µ m). The unstretched film was stretched 4.8 times at a stretching temperature of 135°C in the longitudinal direction, then stretched 1.1 times in the transverse direction and heat-set at 210°C for 30 sec to prepare a 15 µ m-thick stretched polyethylene-2,6-naphthalate film. The stretched polyethylene-2,6-naphthalate film was subjected to corona discharge treatment, and PES-330SK, which is a polyester thermoplastic adhesive manufactured by Toa Gosei Chemical Industry Co., Ltd., was coated thereon. This film was used to heat-seal, at 140°C for 1 sec, a vacuum-formed product (a blister) of vinyl chloride into which a capsule had been packed, thereby preparing a PTP. The results of evaluation of the packaging material for a press-through pack are given in Table A'2. The packaging material for a press-through pack had excellent press-through property, combustibility, and transparency. Examples A'-2 to A'-4 and Reference Example AR'-1: The procedure of Example A'-1 was repeated, except that the intrinsic viscosity of the polyethylene-2,6-naphthalate polymer was varied. The conditions for the preparation of the packaging materials for a press-through pack are specified in Table A'1, and the results of evaluation of the packaging materials for a press-through pack are given in Table A'2. Examples A'-5 to A'-7 and Reference Example AR'-2: The procedure of Example A'-1 was repeated, except that the thickness of the stretched polyethylene-2,6-naphthalate film was varied. The conditions for the preparation of the packaging materials for a press-through pack are specified in Table A'1, and the results of evaluation of the packaging materials for a press-through pack are given in Table A'2. Examples A'-8 and A'-9: The procedure of Example A'-1 was repeated, except that the stretching temperature of the stretched polyethylene-2,6-naphthalate film was varied. The conditions for the preparation of the packaging materials for a press-through pack are specified in Table A'1, and the results of evaluation of the packaging materials for a press-through pack are given in Table A'2. Examples A'-10 to A'-13 and Reference Examples AR'-3 and AR'-4: The procedure of Example A'-1 was repeated, except that the stretch ratio (longitudinal or transverse direction) of the stretched polyethylene-2,6-naphthalate film was varied. The conditions for the preparation of the packaging materials for a press-through pack are specified in Table A'1, and the results of evaluation of the packaging materials for a press-through pack are given in Table A'2. Examples A'-14 to A'-17 and Reference Examples AR'-5 and AR'-6: The procedure of Example A'-1 was repeated, except that the conditions (temperature or time) for heat setting the stretched polyethylene-2,6-naphthalate film were varied. In Reference Example AR'-5, the heat setting was not carried out at all. The conditions for the preparation of the packaging materials for a press-through pack are specified in Table A'1, and the results of evaluation of the packaging materials for a press-through pack are given in Table A'2. Example A'-18 to A'-20 and Comparative Examples AC'-1 to AC'-4: The procedure of Example A'-1 was repeated, except that the material for the vacuum-formed product of the resin or the material for the cover in the packaging material for a press-through pack was varied. The stretching conditions for polypropylene (PP) and polyethylene terephthalate (PET) are those suitable for respective materials. The conditions for the preparation of the packaging materials for a press-through pack are specified in Table A'1, and the results of evaluation of the packaging materials for a press-through pack are given in Table A'2. According to the results of evaluation given in Table A'2, when the stretched polyethylene-2,6-naphthalate film had an intrinsic viscosity of not less than 0.60 (Reference Example AR'-1), a thickness of not less than 150 µ m (Reference Example AR'-2) and a stretch ratio in the transverse direction of not less than 1.8 times (Reference Examples AR'-3 and AR'-4) and was heat-set for not more than 1 sec (Reference Example AR'-5) and heat-set at a temperature of 170°C or below (Reference Example AR'-6), the press-through property was so poor that it was difficult to take out the contents from the press-through pack. When the cover material of the packaging for a press-through pack comprised paper (Comparative Example AC'-1), the packaging material had poor gas barrier property and transparency. When the cover material comprised an aluminum foil, the combustibility and the transparency were poor. Further, when the cover material comprised polyethylene terephthalate (Comparative Example AC'-3) or polypropylene (Comparative Example AC'-4), the press-through property was so poor that it was difficult to take out the contents from the press-through pack. Conditions for preparation of packaging material for press-through pack Intrinsic visco-sity η of PEN as cover material Thickness Stretching temp. Stretch ratio Heat setting Vacuum forming Longitudinal Transverse Temp. Time A'-1 0.41 15 µ 135°C 4.8 1.1 210°C 30sec Vinyl chloride A'-2 0.31 15 µ 135°C 4.8 1.1 210°C 30sec Vinyl chloride A'-3 0.47 15 µ 135°C 4.8 1.1 210°C 30sec Vinyl chloride A'-4 0.58 15 µ 135°C 4.8 1.1 210°C 30sec Vinyl chloride A'-5 0.41 10 µ 135°C 4.8 1.1 210°C 30sec Vinyl chloride A'-6 0.41 30 µ 135°C 4.8 1.1 210°C 30sec Vinyl chloride A'-7 0.41 45 µ 135°C 4.8 1.1 210°C 30sec Vinyl chloride A'-8 0.41 15 µ 140°C 4.8 1.1 210°C 30sec Vinyl chloride A'-9 0.41 15 µ 160°C 4.8 1.1 210°C 30sec Vinyl chloride A'-10 0.41 15 µ 135°C 3.6 1.0 210°C 30sec Vinyl chloride A'-11 0.41 15 µ 135°C 5.3 1.1 210°C 30sec Vinyl chloride A'-12 0.41 15 µ 135°C 4.8 1.0 210°C 30sec Vinyl chloride A'-13 0.41 15 µ 135°C 4.8 1.5 210°C 30sec Vinyl chloride A'-14 0.41 15 µ 135°C 4.8 1.1 180°C 30sec Vinyl chloride A'-15 0.41 15 µ 135°C 4.8 1.1 240°C 30sec Vinyl chloride A'-16 0.41 15 µ 140°C 4.8 1.1 210°C 5sec Vinyl chloride A'-17 0.41 15 µ 135°C 4.8 1.1 210°C 30min Vinyl chloride A'-18 0.41 15 µ 135°C 4.8 1.1 210°C 30sec PEN A'-19 0.41 15 µ 135°C 4.8 1.1 210°C 30sec PP A'-20 0.41 15 µ 135°C 4.8 1.1 210°C 30sec PET AR'-1 0.62 15 µ 135°C 4.8 1.1 210°C 30sec Vinyl chloride AR'-2 0.41 200 µ 135°C 4.8 1.1 210°C 30sec Vinyl chloride AR'-3 0.41 15 µ 135°C 3.5 1.9 210°C 30sec Vinyl chloride AR'-4 0.41 15 µ 135°C 4.8 1.1 - - Vinyl chloride AR'-5 0.41 15 µ 135°C 4.8 1.1 160°C 30sec Vinyl chloride AC'-1 Paper 15 µ - - - - - Vinyl chloride AC'-2 Aluminum foil 20 µ - - - - - Vinyl chloride AC'-3 PET 15 µ 100°C 4.8 1.0 180°C 30sec Vinyl chloride AC'-4 PP 15 µ 150°C 5.2 1.0 170°C 30sec Vinyl chloride Results of evaluation of packaging material for press through pack Pressthrough property 1) Combustibility 2) Gas (oxygen) permeability (cc/m 2 · 24hr·atm) Transparency 3) Press-through of film Strength [kgf] Elongation [mm] A'-1 36.9 1.3 2 A'-2 40.1 1.2 2 A'-3 38.2 1.3 2 A'-4 37.5 1.6 2 A'-5 55.4 1.1 2 A'-6 35.4 1.5 2 A'-7 37.8 1.7 3 A'-8 37.5 1.5 2 A'-9 42.8 1.5 2 A'-10 43.8 2.0 3 A'-11 34.8 1.3 2 A'-12 38.7 1.3 1 A'-13 40.4 1.9 3 A'-14 41.3 1.3 2 A'-15 37.8 1.3 2 A'-16 40.8 1.3 2 A'-17 39.2 1.2 1 A'-18 32.4 1.3 2 A'-19 60.3 1.3 2 A'-20 50.8 1.3 2 AR'-1 40.3 2.2 15 AR'-2 2.9 8.0 27 AR'-3 61.3 2.9 30 AR'-4 36.8 3.2 34 AR'-5 44.3 1.4 38 AR'-6 45.2 1.4 22 AC'-1 Not less than 10000 1.9 2 AC'-2 40.2 1.5 2 AC'-3 57.0 4.2 20 AC'-4 820.3 3.7 20 Examples A'-21 to A'-23: The procedure of Example A'-1 was repeated, except that in the molding of the unstretched film, polypropylene (PP) or polyethylene (PE) was co-extruded to prepare an unstretched film. The unstretched film was treated in the same manner as in Example A'-1, and the PP or PE layer was removed to prepare a stretched polyethylene-2,6-naphthalate film. Thereafter, evaluation was carried out in the same manner as in Example A'-1. The constructions before the removal of the olefin layer are given in Table A'3, the conditions for the preparation of packaging materials for PTP, using stretched PEN films with the olefin layer being removed, are specified in Table A'4, and the results of evaluation of the packaging materials for PTP are given in Table A'5. As a result, the packaging materials for a press-through pack had excellent press-through property, combustibility, gas permeability, and transparency. Construction before removing olefin layer Construction Value within (): film thickness [µm] A'-21 PEN(15)/PP(10) A'-22 PEN(15)/PE(10) A'-23 PEN(20)/PE(10) Conditions for preparation of packaging material for PTP, using stretched PEN film with olefin layer being removed Intrinsic viscosity Thickness Stretching temp. Stretch ratio Heat setting Vacuum forming A'-21 0.41 15 µ 135°C The same as A'-1 Vinyl chloride A'-22 0.41 15 µ 135°C The same as A'-1 Vinyl chloride A'-23 0.41 20 µ 135°C The same as A'-1 Vinyl chloride Results of evaluation of packaging material for PTP Press-through property Combustibility Gas permeability Transparency Press-through of film Strength [kgf] Elongation [mm] A'-21 ○ ○ 36.9 ○ 1.3 2 A'-22 ○ ○ 36.9 ○ 1.3 2 A'-23 ○ ○ 36.9 ○ 1.3 2 Examples A'-24 to A'-30: The procedure of Example A'-1 was repeated, except that a water-vapor barrier resin was laminated to the stretched polyethylene-2,6-naphthalate film and vinyl chloride to be vacuum-formed was coated with vinylidene chloride. The lamination was carried out by extrusion coating (EC, extrusion coating) for Examples A'-24 and A'-25, co-extrusion for Examples A'-26 to A'-28, coating for Example A'-29, and vapor deposition for Example A'-30. The constructions and the water vapor permeability of the stretched PEN films with a water vapor barrier resin being laminated thereto are given in Table A'6. The conditions for the preparation of PTP's using the above packaging materials are specified in Table A'7, and the results of evaluation of the packaging materials for PTP are given in Table A'8. The PTP's prepared in Examples A'-24 and A'-25 and the PTP prepared in Example A'-1 were allowed to stand in an atmosphere kept at 25°C and 90%RH for 15 days. As a result, no moisture absorption was observed for the contents of the PTP's using the packaging materials prepared in A'-24 and A'-25, whereas moisture absorption was observed for the contents of the PTP using the packaging material prepared in Example A'-1. When the PTP's prepared in Examples A'-26 to A'-30 were allowed to stand in an atmosphere kept at 25°C and 90%RH for 30 days, the contents did not absorb any moisture. Construction and water vapor permeability of stretched PEN film with water vapor barrier resin being laminated thereto Construction (value within (): film thickness [µm]) Water vapor permeability [g/m 2 ·24hr] Laminating method A'-24 PEN(15)/AD(2)/PE(12) 30 EC A'-25 PEN(15)/AD(2)/PP(12) 20 EC A'-26 PEN(15)/AD(2)/PE(12) 9 Co-extrusion A'-27 PEN(15)/AD(2)/PP(12) 9 Co-extrusion A'-28 PEN(10)/AD(2)/COC(10) /AD(2)/PEN(10) 15 Co-extrusion A'-29 PEN(15)/PVDC(5) 5 Coat A'-30 PEN(15)/SiO x (200A ) Not more than 0.5 Vapor deposition Conditions for preparation of packaging material for PTP Intrinsic viscosity Thickness Stretching temp. Stretch ratio Heat setting Vacuum forming A'-24 0.41 29 µ 135°C The same as A'-1 Vinyl chloride A'-25 0.41 29 µ 135°C The same as A'-1 Vinyl chloride A'-26 0.41 29 µ 135°C The same as A'-1 Vinyl chloride A'-27 0.41 29 µ 135°C The same as A'-1 Vinyl chloride A'-28 0.41 34 µ 135°C The same as A'-1 Vinyl chloride A'-29 0.41 20 µ 135°C The same as A'-1 Vinyl chloride A'-30 0.41 15 µ 135°C The same as A'-1 Vinyl chloride Results of evaluation of packaging material for PTP Press-through property Combustibility Gas permeability Transparency Press-through of film Strength [kgf] Elongation [mm] A'-24 ○ ○ 36.9 ○ 1.4 3 A'-25 ○ ○ 36.9 ○ 1.4 3 A'-26 ○ ○ 36.9 ○ 1.4 3 A'-27 ○ ○ 36.9 ○ 1.4 3 A'-28 ○ ○ 28.2 ○ 1.5 4 A'-29 ○ ○ 10.0 ○ 1.3 3 A'-30 ○ ○ Not more than 0.5 ○ 1.3 2 Examples A'-31 to A'-35: The procedure of Example A'-1 was repeated, except that an oxygen barrier resin was laminated to the stretched polyethylene-2,6-naphthalate film, vinyl chloride to be vacuum-formed was coated with vinylidene chloride and the contents of the pack were solid fats and oils. The lamination was carried out by co-extrusion. In Example A'-34 and A'-35, the PTP packaging in Examples A'-29 and A'-30 was used, and the contents were solid fats and oils. The adhesive layer comprised a modified polyester adhesive resin for the co-extrusion. The constructions and the gas permeability of the stretched PEN films with an oxygen barrier resin being laminated thereto are given in Table A'9. The conditions for the preparation of the packaging materials for PTP are specified in Table A'10, and the results of evaluation of the packaging materials for PTP are given in Table A'11. The PTP's prepared in Examples A'-31 to A'-35 and the PTP prepared in Example A'-1 were allowed to stand in an atmosphere kept at 25°C and 50%RH for 30 days. As a result, it was found that the contents of the PTP's using the packaging materials prepared in Examples A'-31 to A'-35 were not oxidized, whereas the contents of the PTP using the packaging material prepared in Example A'-1 were oxidized. Construction of stretched PEN film with gas barrier resin being laminated thereto Construction (value within (): film thickness [µm]) Laminating method A'-31 PEN(15)/AD(2)/PVA(12) Co-extrusion A'-32 PEN(15)/AD(2)/EVOH(12) Co-extrusion A'-33 PEN(15)/AD(2)/EVOH(5)/AD(2)/PEN(10) Co-extrusion A'-34 PEN(15)/PVDC(5) Coating A'-35 PEN(15)/SiO x (200A ) Vapor deposition Conditions for preparation of packaging material for PTP Intrinsic viscosity Thickness Stretching temp. Stretch ratio Heat setting Vacuum forming A'-31 0.41 29 µ 135°C The same as A'-1 Vinyl chloride A'-32 0.41 29 µ 135°C The same as A'-1 Vinyl chloride A'-33 0.41 29 µ 135°C The same as A'-1 Vinyl chloride A'-34 0.41 20 µ 135°C The same as A'-1 Vinyl chloride A'-35 0.41 15 µ 135°C The same as A'-1 Vinyl chloride Results of evaluation of packaging material for PTP Press-through property Combustibility Gas permeability Transparency Press-through of film Strength [kgf] Elongation [mm] A'-31 ○ ○ 4 ○ 1.4 3 A'-32 ○ ○ 4 ○ 1.5 4 A'-33 ○ ○ 10 ○ 1.5 3 A'-34 ○ ○ 5 ○ 1.3 3 A'-35 ○ ○ Not more than 0.5 ○ 1.3 2 Examples A'-36 and A'-37: The procedure of Example A'-1 was repeated, except that a water-vapor barrier resin and an oxygen barrier resin were laminated to the stretched polyethylene-2,6-naphthalate film, vinyl chloride to be vacuum-formed was coated with vinylidene chloride and the contents were a hygroscopic chemical. The adhesive layer comprised a modified polyester adhesive resin for the co-extrusion. The constructions and the water vapor permeability of the stretched PEN films with a water-vapor barrier resin and an oxygen barrier resin being laminated thereto are given in Table A'12. The conditions for the preparation of the packaging materials for PTP are specified in Table A'13, and the results of evaluation of the packaging materials for PTP are given in Table A'14. The PTP's using the packaging materials prepared in Examples A'-36 and A'-37 and the PTP using the packaging material prepared in Example A'-1 were allowed to stand in an atmosphere kept at 25°C and 90%RH for 30 days. As a result, it was found that neither moisture absorption nor oxidation occurred for the contents of the PTP's using the packaging materials prepared in Examples A'-36 and A'-37, whereas moisture absorption and oxidation occurred for the contents of the PTP using the packaging material prepared in Example A'-1. Construction of stretched PEN film with water vapor barrier resin and oxygen barrier resin being laminated thereto Construction Value within (): film thickness [µm] Water vapor permeability [g/m 2 ·24hr] Laminating method A'-36 PEN(15)/AD(2)/EVOH(5)/ AD(2)/PE(12) 30 Co-extrusion A'-37 PEN(15)/AD(2)/PVA(12)/ AD(2)/PE(12) 30 Co-extrusion Conditions for preparation of packaging material for PTP Intrinsic viscosity Thickness Stretching temp. Stretch ratio Heat setting Vacuum forming A'-36 0.41 36 µ 135°C The same as A'-1 Vinyl chloride A'-37 0.41 43 µ 135°C The same as A'-1 Vinyl chloride Results of evaluation of packaging material for PTP Press-through property Combustibility Gas permeability Transparency Press-through of film Strength [kgf] Elongation [mm] A'-36 ○ ○ 9 ○ 1.4 4 A'-37 ○ ○ 9 ○ 1.4 4 Examples A'-38 to A'-40: In Examples A'-38 to A'-40, Examples A'-1 was repeated, except that the thickness of the stretched polyethylene-2,6-naphthalate film was varied, a protective layer of PE was laminated and the contents were a cell (⊘16 x 33 mm). The lamination was carried out by EC or co-extrusion. The constructions of the stretched PEN films with a protective layer being laminated thereto are given in Table A'15. The conditions for the preparation of the packaging materials for PTP are specified in Table A'16, and the results of evaluation of the packaging materials for PTP are given in Table A'17. The packaging materials for a press-through pack had excellent press-through property, combustibility, gas permeability, and transparency. Construction of stretched PEN film with protective layer being laminated thereto Construction Value within (): film thickness [µm] Laminating method A'-38 PEN(10)/AD(2)/PE(10) Co-extrusion A'-39 PEN(10)/AD(2)/PE(20) EC A'-40 PEN(10)/AD(2)/PE(50) EC Conditions for preparation of packaging material for PTP Intrinsic viscosity Thickness Stretching temp. Stretch ratio Heat setting Vacuum forming A'-38 0.41 22 µ 135°C The same as A'-1 Vinyl chloride A'-39 0.41 32 µ 135°C The same as A'-1 Vinyl chloride A'-40 0.41 62 µ 135°C The same as A'-1 Vinyl chloride Results of evaluation of packaging material for PTP Press-through property Combustibility Gas permeability Transparency Press-through of film Strength [kgf] Elongation [mm] A'-38 ○ ○ 55 ○ 1.2 3 A'-39 ○ ○ 55 ○ 1.4 3 A'-40 ○ ○ 55 ○ 1.4 5 Examples A'-41 to A'-43: The procedure of Examples A'-1 was repeated, except that the thickness of the stretched polyethylene-2,6-naphthalate film was varied, a water-vapor barrier resin and/or an oxygen barrier resin were laminated to the film, a protective layer was further laminated, vinyl chloride to be vacuum-formed was coated with vinylidene chloride and the contents were a hygroscopic chemical. The adhesive layer comprised a polyester AC agent for EC and a modified polyester adhesive resin for co-extrusion. The constructions and the water-vapor permeability of the stretched PEN films with a water-vapor barrier resin and/or an oxygen barrier resin and a protective layer being laminated thereto are given in Table A'18. The conditions for the preparation of the packaging materials for PTP are specified in Table A'19, and the results of evaluation of the packaging materials for PTP are given in Table A'20. The PTP's using the packaging materials prepared in Examples A'-41 to A'-43 and the PTP using the packaging material prepared in Example A'-1 were allowed to stand in an atmosphere kept at 25°C and 90%RH for 30 days. As a result, no moisture absorption was observed for the contents of the PTP's using the packaging materials prepared in Examples A'-41 and A'-43, whereas moisture absorption was observed for the contents of PTP using the packing material prepared in Examples A'-1. The PTP's using the packaging materials prepared in Examples A'-41 to A'-43 and the PTP using the packaging material prepared in Example A'-1 were allowed to stand in an atmosphere kept at 25°C and 50%RH for 30 days. As a result, it was found that no oxidation occurred for the contents of the PTP's using the packaging materials prepared in Examples A'-42 and A'-43, whereas oxidation occurred for the contents of the PTP using the packing material prepared in Examples A'-1. Construction of stretched PEN film with water vapor barrier resin or oxygen barrier resin or both water vapor barrier resin and oxygen barrier resin and protective layer being laminated thereto Construction Value within (): film thickness [µm] Water vapor permeability [g/m 2 ·24hr] Laminating method A'-41 PEN(7)/AD(2)/COC(10)/ AD(2)/PE(12) 10 Co-extrusion A'-42 PEN(7)/AD(2)/EVOH(5)/ AD(2)/PE(12) 20 Co-extrusion A'-43 PEN(7)/AD(2)/PVA(10)/ AD(2)/COC(10)/AD(2)/ PE(12) 10 Co-extrusion Conditions for preparation of packaging material for PTP Intrinsic viscosity Thickness Stretching temp. Stretch ratio Heat setting Vacuum forming A'-41 0.41 33 µ 135°C The same as A'-1 Vinyl chloride A'-42 0.41 28 µ 135°C The same as A'-1 Vinyl chloride A'-43 0.41 45 µ 135°C The same as A'-1 Vinyl chloride Results of evaluation of packaging material for PTP Press-through property Combustibility Gas permeability Transparency Press-through of film Strength [kgf] Elongation [mm] A'-41 ○ ○ 75 ○ 1.4 4 A'-42 ○ ○ 10 ○ 1.4 4 A'-43 ○ ○ 5 ○ 1.4 4 Examples A'-44 to A'-46 and Reference Example AR'-8: The procedure of Examples A'-1 was repeated, except that the thickness of the stretched polyethylene-2,6-naphthalate film was varied and the contents were a working cutter (length: 150 mm). The conditions for the preparation of the packaging materials for PTP are specified in Table A'21, and the results of evaluation of the packaging materials for PTP are given in Table A'22. In Reference Example AR'-8, it was difficult to take out the contents from the press-through pack. Conditions for preparation of packaging material for PTP Intrinsic viscosity Thickness Stretching temp. Stretch ratio Heat setting Vacuum forming A'-44 0.41 20 µ 135°C The same as A'-1 Vinyl chloride A'-45 0.41 45 µ 135°C The same as A'-1 Vinyl chloride A'-46 0.41 150 µ 135°C The same as A'-1 Vinyl chloride AR'-8 0.41 200 µ 135°C The same as A'-1 Vinyl chloride Results of evaluation of packaging material for PTP Pressthrough property Combustibility Gas permeability Transparency Press-through of film Strength [kgf] Elongation [mm] A'-44 ○ ○ 28 ○ 1.4 2 A'-45 ○ ○ 12 ○ 1.7 3 A'-46 ○ ○ 4 ○ 4.4 7 AR'-8 X ○ 3 ○ 8.0 27

Claims: A press-through pack (PTP) or a blister pack comprising a holding portion and a cover film, said film comprising a resin composed mainly of polyethylene-2,6-naphthalate and having an intrinsic viscosity η in the range of from 0.31 to 0.6. The PTP or blister pack according to claim 1, wherein the film has stretch ratios of 1 to 3 times and 1 to 3 times respectively in substantially mutually perpendicular directions and a thickness in the range of from 5 to 150 µ m. The PTP or blister pack according to claim 1, wherein the film has stretch ratios of 3 to 6 times and 1 to 1.8 times respectively in substantially mutually perpendicular directions and a thickness in the range of from 5 to 150 µ m. The PTP or blister pack according to any one of claims 1 to 3, wherein the film further comprises a water vapor barrier layer and/or an oxygen barrier layer laminated thereto. The PTP or blister pack according to any one of claims 1 to 4, wherein the film further comprises a reinforcing layer comprising a synthetic resin, said reinforcing layer being laminated to at least one side of said film. The PTP or blister pack according to any one of claims 1 to 5, wherein the film further comprises a heat-sealed layer or an adhesive layer laminated thereto. The PTP or blister pack according to any one of claims 1 to 6, wherein the film further comprises a printed layer of a printing ink laminated thereto. A process for producing the PTP or blister pack of claim 2, comprising the steps of: providing a resin material comprising polyethylene-2,6-naphthalate having an intrinsic viscosity η in the range of from 0.31 to 0.6, stretching the resin material at 120 to 270°C in substantially mutually perpendicular directions respectively by 1 to 3 times and 1 to 3 times, heat-treating the stretched resin material at 170 to 270°C for 1 sec to 30 min to heat-set the resin material, molding the heat-set resin material into a film having a final thickness in the range of from 5 to 150 µ m, and bonding the film to the holding portion with an adhesive or a heat-sealing agent. A process for producing the PTP or blister pack of claim 3, comprising the steps of: providing a resin material comprising polyethylene-2,6-naphthalate having an intrinsic viscosity η in the range of from 0.31 to 0.6, stretching the resin material at 120 to 170°C in substantially mutually perpendicular directions respectively by 3 to 6 times and 1 to 1.8 times, heat-treating the stretched resin material at 170 to 260°C for 1 sec to 30 min to heat-set the resin material, molding the heat-set resin material into a film having a final thickness in the range of from 5 to 150 µ m, and bonding the film to the holding portion with an adhesive or a heat-sealing agent. A process for producing the PTP or blister pack of claim 1, comprising the steps of: co-extruding a polyethylene-2,6-naphthalate resin having an intrinsic viscosity η in the range of from 0.31 to 0.6 and a synthetic resin, stretching and heat-treating the co-extrudate by a process according to claim 8 or 9, removing said synthetic resin layer, molding the remaining layer into a film having a final thickness in the range of from 5 to 150 µ m, and bonding the film to the holding portion with an adhesive or a heat-sealing agent.

Inventors: HARADA YASUHIRO, HASEGAWA KAYO, INOUE ISAO, KUMAKI CHIKAO, MORI SHINICHIRO, SASADA KATSUHIKO, SUZUKI TOSHIYUKI, SUZUURA YASUKI, YAMAGUCHI MASAHISA, YAMASHITA RIKIYA, HARADA, YASUHIRO, HASEGAWA, KAYO, INOUE, ISAO, KUMAKI, CHIKAO, MORI, SHINICHIRO, SASADA, KATSUHIKO, SUZUKI, TOSHIYUKI, SUZUURA, YASUKI, YAMAGUCHI, MASAHISA, YAMASHITA, RIKIYA, INOUE, ISAO DAI NIPPON PRINTING CO., LTD., SUZUKI, TOSHIYUKI DAI NIPPON PRINTING CO., LTD., SUZUURA, YASUKI DAI NIPPON PRINTING CO., LTD., YAMAGUCHI, MASAHISA DAI NIPPON PRINTING CO., LTD., YAMASHITA, RIKIYA DAI NIPPON PRINTING CO., LTD.
Applicants: DAINIPPON PRINTING CO LTD, NIPPON KOKAN KK, DAI NIPPON PRINTING CO., LTD., NKK CORPORATION
Application year: 1994
Main classification: C08J5
IPC codes: B32B27, B29C55, C08L67, C08G63, C08J5